explain xkcd - User contributions [en]

User:IdiosyncraticLawyer

2022-02-25T09:54:26Z

172.70.142.239:

==Add a Title. Stay Safe; Stay Well.==
I registered my Explain xkcd account at 19:59, 10/01/2022, and confirmed my email at 02:52 on 11/01/2022. As of 19:59, 13/01/2022, I am an autoconfirmed user.

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Countdown in header text

2022-01-21T01:12:53Z

172.70.142.239:

{{comic
| date = January 10, 2022
| title = Countdown in header text
| image = Countdown_in_header_text.png
| before = The countdown will probably last 21 days. After February 1st 2022 it is likely to have disappeared. See this [https://web.archive.org/web/20220110183238/https://xkcd.com/ 2022-01-10] archive version.
| ldomain = www
| lappend =
| extra = yes
}}
*Go directly to the list of [[Countdown in header text/images|images]].
**The images can also be found [https://munvoseli.github.io/xkcd-countdown/ here] on munvoseli's page where comparison of two images and an animation can be seen.
{{TOC}}
==Explanation==
*On January 10th 2022, [[Randall]] added a countdown in the top right corner of the [[xkcd Header text]] on {{xkcd}}.
**This happened while the comic [[2565: Latency]] was up.
***First the xkcd Header text was [[xkcd_Header_text#2022-01-08_-_Back_to_standard_text|changed back]] to the [[xkcd_Header_text#Header_text|standard text]] for the first time in almost three years:
****xkcd updates every Monday, Wednesday, and Friday.
***But already while this Friday-comic was still up on the following Monday the [[xkcd_Header_text#2022-01-10_-_Standard_text_with_countdown|countdown]] was added.
****This was thus up when the Monday comic [[2566: Decorative Constants]] was released, drawing more people to the xkcd page.
*The first [[#Archived Versions|archived version]] from [https://web.archive.org/web/20220110183238/https://xkcd.com/ 2022-01-10] read 20d 20h 27m.
**It looks like it started on [https://munvoseli.github.io/xkcd-countdown/ 01-10 17:00 UTC].
***At that time it would have read 20d 21h 59 min. Just two hours and 1 minute short of 3 weeks.
*This countdown will reach zero on Monday 2022-01-31 at 14:59 (2:59 PM) {{w|UTC}}, or 9:59 AM in Boston, Randall's home town.
**If seconds will be added towards the end, it seems likely that it may end exactly at 15:00 UTC (10:00 AM in Boston).
***However, if it's using EST, introduced in comic [[1061: EST]], it would count backward for four hours before reaching zero, and end only at 2022-01-31 23:59 UTC
****This is extremely farfetched though!
****Though either way, it would fall on Monday 2022-01-31, and therefore the day comic 2575 should be released.
*The next day on [https://web.archive.org/web/20220111153818/https://xkcd.com/ 2022-01-11] a diagonal black bar appeared in the lower left-hand corner of the countdown box and started to move further into the image on following changes to the [[#Images|image]].
**This development called for the creation of this dedicated [[Countdown in header text]] page.
**The line had already moved further into the image at this time, but the latest version will never be available in the web archive.
***This development is reminiscent of the huge comic [[1190: Time]].
*As mentioned above, [https://munvoseli.github.io/ Munvoseli] is keeping [https://munvoseli.github.io/xkcd-countdown/ track of the changes] to the image on the countdown.
**Although there are (at 2022-01-12 12:35 UTC) thirteen different frames we know of, the first three looks the same (because the diagonal bar was not in the frame yet) and the seventh and the eighth also seems to be the same, even though the bar had already begun moving across the frame from the fourth. This is either on purpose, a slipup or means that The FrameTM might not be zooming out of a larger image.
***However, the images that look the same all have individual addresses on the xkcd server. See more under [[#Images|Images]] below.

Randall has previously made a comic simply called [[1159: Countdown]]. However, in that the roles are reversed. There we know that the countdown is for (Super Volcano) but not if it will happen soon or very much later. Here we know when, and it is rather soon, but not what.

==Images==
*Images will be put on [[Countdown in header text/images|this separate page]].
**The images can also be found [https://munvoseli.github.io/xkcd-countdown/ here] on munvoseli's page.
***It is possible to compare two images, chosen between those released, on that page!
***From 2022-01-14 it has also been possible to see an animation.
**See more details at the top of the image page.
*After a few days the black lines forming the image came into conflict with the clock, which has a rounded white frame around it. This can be seen in one of the earliest examples here:
[[File:Countdown in header text Clock Cover Black Lines.png]]
*Also at this time a new development happened after the "plane tail" moved forward it stopped on 2022-01-18 and started moving up (or zooming in). See for instance these two comparison from munvoseli's page showing the difference from the 8 pictures before today, and then after three out today:
[[File:Countdown in header text Compare 40 to 48.png]] [[File:Countdown in header text Compare 48 to 51.png]]

==Theories==
*Here different theories for what the countdown is for and what the picture is going to reveal can be added.

===The picture===
* Ongoing description:
** Frames 1-12: A diagonal line.
** Frame 13: A curve seems to begin at the top left of the line.
** Frame 18: The curve connects the diagonal line with a horizontal line.
** Frame 27-28: A new line appears in the bottom left corner.
** Frame 40-42: The new line turns out to be connected to the horizontal line, forming a corner which is not attached to any other line.
** Frame 49: The "camera movement" direction changes, while the object is still moving upward it stopped moving towards the left side, moving towards the right instead.
** Frame 54: A slight upward curve seems to appear in the right line, the left line seems to have a small bend downwards, though that could at that point just be a straight line that randall drew without a ruler.
** Frame 60-62: A new line appears in the bottom right corner, it turns out to be a continuation of the first original line which curves upward and has a positive slope at that point of the picture, between about 2 o'clock and 3 o'clock. The downward bend of the left line continues on straight in the same direction, it was probably an intentional bend and not an irregularity in drawing a straight line by hand.
** Frame 63: In the minimum of the right curved line a new line starts appearing, way thinner than the others (which were up to this point all rather part of one line) and going slightly downwards and very much to the left, at an angle somewhere between 8 o'clock and 9 o'clock.
** Frame 67: A possible feature becomes visible at the bottom edge of the image that might resolve the exact nature of the (currently presumed) aircraft, e.g. which particular aerodynamic surface we have been seeing and thus from which particular orientation we are viewing it.


*Theories about the picture:
**It seems after two days and 12 pictures like either something is moving into the frame or that it is a zoom out from a white area of a large picture. Maybe it is the arm of Cueball that will come into view.
***That turned out not to be the case!
**The second line makes it look somewhat like the tail fin of an aircraft.
***Or the wing of an aircraft (left if looking down at it). Perhaps the plane is towing a banner that will fly through the frame.
****After almost a week this looks like the most promising suggestion so far.
*****Now that the direction of the camera movement has changed, we might get to see the rest of the aircraft soon.
******From picture 63, it more and more seems like it was the tail fin of a plane and now we can see the body.
*******It's almost certainly the tail (and now a bit of the rear fuselage) of an aircraft.
****Tail of a space shuttle, perhaps?
*****While I think Randall would've also drawn in the signature black part of the rudder, the shape fits perfectly
*****Timing is close (though not exact) to the Columbia disaster anniversary (2003-02-01 1359 UTC)
****I'm thinking the tail of a Zeppelin.
*****Although those normally have longer tail fins.
**Maybe it is some kind of vehicle rolling into frame, like a car?
***No
**Or the word xkcd? (or xkcd 2?)
***No
**Could have been "Hangman", but it looks like it's zooming in on the diagonal instead of continuing to make a gibbet.
***No
**With the new second line appearing in the corner as of frame 28 it looks like it's definitely zooming out of an image. It looks like it could be someone's arm in a running position.
***No
**I think it could also be two legs of a reclining stick person.
***No
**The lines suggest a shark fin and the movement would suggest it swimming across the frame.
***If it was a shark fin, then the most likely candidates would be the first dorsal fin and the pectoral fin, but both end in points rather than edges like in the pictures of the header puzzle. An aircraft tail fin still seems most likely.
**Maybe it's a two-dimensional shape viewed from a weird angle?
***Like a rectangle viewed from a floating, tilted perspective
****No
***Or the top of the k in xkcd
****No
***Or a boat dock?
****No
**How about the [https://www.hitc.com/en-gb/2021/09/09/star-trek-picard-season-2-release-date-plot-cast/ new series of Picard]?

===Countdown===
*Theories about the countdown:
*Several have already been mentioned in the discussion:
**Randall's next book, either the countdown is counting down to the start of promotion or it is released when the countdown ends.
***Usually Randall has made month long [[:Category:Book promotion|book promotions]] before release. So if it is the release day it is a new way to do it. But he will get a lot of attention. If it is just the start of promoting it, people might get disappointed…
****For instance he began promoting his [[xkcd_Header_text#2015-05-14_-_New_book_Thing_Explainer|new book Thing Explainer]] in the header text. That was in May 2015 and the book was first released [https://blog.xkcd.com/2015/05/13/new-book-thing-explainer/ late November 2015]. Most of this time the header text was promoting the book.
**{{w|James Webb Space Telescope}} (JWST) going into orbit about L2 {{w|Lagrange point}}.
***Randall has already made several comics about the telescope. The latest [[2564: Sunshield]] was released just five days prior to the countdown was started.
***But the telescope will not reach the point but rather go into a large orbit around it, so a precise timer counting down to it seems a bit farfetched.
***On NASA's page on JWST it seems like it will [https://www.jwst.nasa.gov/content/webbLaunch/deploymentExplorer.html#25 go into orbit] 29.5 days after its [[December 25th Launch]], on Christmas Day, so it should have already started the orbit by the 23rd or 24th of January - 8 days before the countdown.
**{{w|Lunar New Year}}
***In China it starts on February 1st and a [https://yourcountdown.to/chinese-new-year countdown for China] is 8 hours behind.
****The South Korean time zone is UTC+9, hence 14:59 UTC = 23:59 in South Korea, one minute to Feb 1.
*****But it's weird if Randall that has basically never mentioned this holiday suddenly makes a three week countdown for it, and why choose South Korea when most would think of China in this context…?
**Randall will stop making xkcd (Goodbye in the image).
***Hopefully not.
****Agreed, {{tvtropes|PoisonOakEpilepticTrees|to be avoided}}
**[https://nationaldaycalendar.com/backward-day-january-31/ National Backward Day]
***This is not a day mentioned on Wikipedia at the time of release of the countdown, so seems unlikely.
**Maybe it will be an announcement of xkcd 2, a new and improved version for… some reason?
***Seems unlikely…
**{{w|Black History Month}}. The {{w|Greensboro sit-ins}} started on Feb 1 1960. Black History Month also begins on February 1st, also in 2022.
***But this countdown stops early on January 31st so seems unlikely.
***However, before changing the Header recently it was about [[xkcd_Header_text#2020-06-03_-_Black_Lives_Matter|Black Lives Matter]] for more than 1.5 years, first ending on December 20th 2021, less than a month before the countdown began. In between that there was a short Christmas sale reminder until a week into 2022. So it could just be another way of reminding of us the issues faced by black people in the US.
****If this was true, I feel like it would be simpler to just change back to the Black Lives Matter text at the top of the screen. Also, it seems increasingly likely as of Jan. 20th that the image is some kind of plane, which doesn't really have much to do with Black History Month (that I know of?)
**The accompanying header says specifically "xkcd updates Monday, Wednesday, and Friday"--maybe the countdown is to the reveal of a new update schedule?
***Very unlikely. This was the standard header for a long time. It was used when Randall had nothing better to say. But with all his books and the trouble in US with elections and BLM, he has used the header as a platform most of the time many years now. So the standard text is rare. But he did return it for two days before adding the count down, making it seem just like normal.
***A guess is that it returned to this, so the header text did not take any focus away from the countdown.
**[[:Category:Red Spiders|Red spider]] attack?
***Un-Likely
**He will become a father - could be a planned C-section.
***As this is unpredictable, and could go wrong, then this would be a dangerous countdown, people can be very superstitious, even if scientist.
**As it currently looks (after a [[1070: Words for Small Sets|few days]] into the countdown) it may be a trip he is taking by plane.
***Maybe going somewhere people could meet him.
****Book tour?
***Moving a long way from home (down under or the like).
****Maybe he's moving to Japan? Could be a plane, and the time zone would fit, at least.
*****Then the countdown would be until when the plane lands, not to midnight.
****What has time zones to do with this clock? It counts down to the same time all over the world, and will reach zero at the same time no matter what time zone you are in.
*****Time zones have to do with where it will be midnight when the countdown reaches zero. If it's a countdown to when January ends (a moment before February begins), then it's until that moment in the time zone where the countdown reaches zero at that time.
**Perhaps it's a start to a new series like [[1190: Time]].
***It is already a series that works like Time, so seems unlikely.
**Zero-G flight, really looks like plane to me.
***Could be time he will first go weightless which could be fairly well known except for bad weather

==Archived Versions==
*Here is a list of the versions that has been saved to the web archive during the countdown.
**The counter in that version is written behind the date of the web archive.
**Note that the counter is active on the archived version counting minutes down from the start. Some of the versions almost changing the minutes just after loading. But it will always count from the time given here:
#[https://web.archive.org/web/20220110183238/https://xkcd.com/ 2022-01-10] 20d 20h 27m
#[https://web.archive.org/web/20220110214138/https://xkcd.com/ 2022-01-10] 20d 17h 18m
#[https://web.archive.org/web/20220111011115/https://xkcd.com/ 2022-01-11] 20d 13h 48m
#[https://web.archive.org/web/20220112005828/https://xkcd.com/ 2022-01-12] 19d 14h 1m
#[https://web.archive.org/web/20220113044552/https://xkcd.com/ 2022-01-13] 18d 10h 14m
#[https://web.archive.org/web/20220114010759/https://xkcd.com/ 2022-01-14] 17d 13h 51m
#[https://web.archive.org/web/20220114195624/https://xkcd.com/ 2022-01-14] 16d 19h 3m
#[https://web.archive.org/web/20220115052737/https://xkcd.com/ 2022-01-15] 16d 9h 32m
#[https://web.archive.org/web/20220116074923/https://xkcd.com/ 2022-01-16] 15d 7h 10m
#[https://web.archive.org/web/20220116225217/https://xkcd.com/ 2022-01-16] 14d 16h 7m
#[https://web.archive.org/web/20220118050255/https://xkcd.com/ 2022-01-18] 13d 9h 57m
#[https://web.archive.org/web/20220119213308/https://xkcd.com/ 2022-01-19] 11d 17h 26m

{{comic discussion}}

[[Category:Meta]]

Countdown in header text

2022-01-21T01:12:11Z

172.70.142.239:

{{comic
| date = January 10, 2022
| title = Countdown in header text
| image = Countdown_in_header_text.png
| before = The countdown will probably last 21 days. After February 1st 2022 it is likely to have disappeared. See this [https://web.archive.org/web/20220110183238/https://xkcd.com/ 2022-01-10] archive version.
| ldomain = www
| lappend =
| extra = yes
}}
*Go directly to the list of [[Countdown in header text/images|images]].
**The images can also be found [https://munvoseli.github.io/xkcd-countdown/ here] on munvoseli's page where comparison of two images and an animation can be seen.
{{TOC}}
==Explanation==
*On January 10th 2022, [[Randall]] added a countdown in the top right corner of the [[xkcd Header text]] on {{xkcd}}.
**This happened while the comic [[2565: Latency]] was up.
***First the xkcd Header text was [[xkcd_Header_text#2022-01-08_-_Back_to_standard_text|changed back]] to the [[xkcd_Header_text#Header_text|standard text]] for the first time in almost three years:
****xkcd updates every Monday, Wednesday, and Friday.
***But already while this Friday-comic was still up on the following Monday the [[xkcd_Header_text#2022-01-10_-_Standard_text_with_countdown|countdown]] was added.
****This was thus up when the Monday comic [[2566: Decorative Constants]] was released, drawing more people to the xkcd page.
*The first [[#Archived Versions|archived version]] from [https://web.archive.org/web/20220110183238/https://xkcd.com/ 2022-01-10] read 20d 20h 27m.
**It looks like it started on [https://munvoseli.github.io/xkcd-countdown/ 01-10 17:00 UTC].
***At that time it would have read 20d 21h 59 min. Just two hours and 1 minute short of 3 weeks.
*This countdown will reach zero on Monday 2022-01-31 at 14:59 (2:59 PM) {{w|UTC}}, or 9:59 AM in Boston, Randall's home town.
**If seconds will be added towards the end, it seems likely that it may end exactly at 15:00 UTC (10:00 AM in Boston).
***However, if it's using EST, introduced in comic [[1061: EST]], it would count backward for four hours before reaching zero, and end only at 2022-01-31 23:59 UTC
****This is extremely farfetched though!
****Though either way, it would fall on Monday 2022-01-31, and therefore the day comic 2575 should be released.
*The next day on [https://web.archive.org/web/20220111153818/https://xkcd.com/ 2022-01-11] a diagonal black bar appeared in the lower left-hand corner of the countdown box and started to move further into the image on following changes to the [[#Images|image]].
**This development called for the creation of this dedicated [[Countdown in header text]] page.
**The line had already moved further into the image at this time, but the latest version will never be available in the web archive.
***This development is reminiscent of the huge comic [[1190: Time]].
*As mentioned above, [https://munvoseli.github.io/ Munvoseli] is keeping [https://munvoseli.github.io/xkcd-countdown/ track of the changes] to the image on the countdown.
**Although there are (at 2022-01-12 12:35 UTC) thirteen different frames we know of, the first three looks the same (because the diagonal bar was not in the frame yet) and the seventh and the eighth also seems to be the same, even though the bar had already begun moving across the frame from the fourth. This is either on purpose, a slipup or means that The FrameTM might not be zooming out of a larger image.
***However, the images that look the same all have individual addresses on the xkcd server. See more under [[#Images|Images]] below.

Randall has previously made a comic simply called [[1159: Countdown]]. However, in that the roles are reversed. There we know that the countdown is for (Super Volcano) but not if it will happen soon or very much later. Here we know when, and it is rather soon, but not what.

==Images==
*Images will be put on [[Countdown in header text/images|this separate page]].
**The images can also be found [https://munvoseli.github.io/xkcd-countdown/ here] on munvoseli's page.
***It is possible to compare two images, chosen between those released, on that page!
***From 2022-01-14 it has also been possible to see an animation.
**See more details at the top of the image page.
*After a few days the black lines forming the image came into conflict with the clock, which has a rounded white frame around it. This can be seen in one of the earliest examples here:
[[File:Countdown in header text Clock Cover Black Lines.png]]
*Also at this time a new development happened after the "plane tail" moved forward it stopped on 2022-01-18 and started moving up (or zooming in). See for instance these two comparison from munvoseli's page showing the difference from the 8 pictures before today, and then after three out today:
[[File:Countdown in header text Compare 40 to 48.png]] [[File:Countdown in header text Compare 48 to 51.png]]

==Theories==
*Here different theories for what the countdown is for and what the picture is going to reveal can be added.

===The picture===
* Ongoing description:
** Frames 1-12: A diagonal line.
** Frame 13: A curve seems to begin at the top left of the line.
** Frame 18: The curve connects the diagonal line with a horizontal line.
** Frame 27-28: A new line appears in the bottom left corner.
** Frame 40-42: The new line turns out to be connected to the horizontal line, forming a corner which is not attached to any other line.
** Frame 49: The "camera movement" direction changes, while the object is still moving upward it stopped moving towards the left side, moving towards the right instead.
** Frame 54: A slight upward curve seems to appear in the right line, the left line seems to have a small bend downwards, though that could at that point just be a straight line that randall drew without a ruler.
** Frame 60-62: A new line appears in the bottom right corner, it turns out to be a continuation of the first original line which curves upward and has a positive slope at that point of the picture, between about 2 o'clock and 3 o'clock. The downward bend of the left line continues on straight in the same direction, it was probably an intentional bend and not an irregularity in drawing a straight line by hand.
** Frame 63: In the minimum of the right curved line a new line starts appearing, way thinner than the others (which were up to this point all rather part of one line) and going slightly downwards and very much to the left, at an angle somewhere between 8 o'clock and 9 o'clock.
** Frame 67: A possible feature becomes visible at the bottom edge of the image that might resolve the exact nature of the (currently presumed) aircraft, e.g. which particular aerodynamic surface we have been seeing and thus from which particular orientation we are viewing it.


*Theories about the picture:
**It seems after two days and 12 pictures like either something is moving into the frame or that it is a zoom out from a white area of a large picture. Maybe it is the arm of Cueball that will come into view.
***That turned out not to be the case!
**The second line makes it look somewhat like the tail fin of an aircraft.
***Or the wing of an aircraft (left if looking down at it). Perhaps the plane is towing a banner that will fly through the frame.
****After almost a week this looks like the most promising suggestion so far.
*****Now that the direction of the camera movement has changed, we might get to see the rest of the aircraft soon.
******From picture 63, it more and more seems like it was the tail fin of a plane and now we can see the body.
*******It's almost certainly the tail (and now a bit of the rear fuselage) of an aircraft.
****Tail of a space shuttle, perhaps?
*****While I think Randall would've also drawn in the signature black part of the rudder, the shape fits perfectly
*****Timing is close (though not exact) to the Columbia disaster anniversary (2003-02-01 1359 UTC)
****I'm thinking the tail of a Zeppelin.
*****Although those normally have longer tail fins.
**Maybe it is some kind of vehicle rolling into frame, like a car?
***No
**Or the word xkcd? (or xkcd 2?)
***No
**Could have been "Hangman", but it looks like it's zooming in on the diagonal instead of continuing to make a gibbet.
***No
**With the new second line appearing in the corner as of frame 28 it looks like it's definitely zooming out of an image. It looks like it could be someone's arm in a running position.
***No
**I think it could also be two legs of a reclining stick person.
***No
**The lines suggest a shark fin and the movement would suggest it swimming across the frame.
***If it was a shark fin, then the most likely candidates would be the first dorsal fin and the pectoral fin, but both end in points rather than edges like in the pictures of the header puzzle. An aircraft tail fin still seems most likely.
**Maybe it's a two-dimensional shape viewed from a weird angle?
***Like a rectangle viewed from a floating, tilted perspective
****No
***Or the top of the k in xkcd
****No
***Or a boat dock?
****No
**How about the [https://www.hitc.com/en-gb/2021/09/09/star-trek-picard-season-2-release-date-plot-cast/ new series of Picard]?

===Countdown===
*Theories about the countdown:
*Several have already been mentioned in the discussion:
**Randall's next book, either the countdown is counting down to the start of promotion or it is released when the countdown ends.
***Usually Randall has made month long [[:Category:Book promotion|book promotions]] before release. So if it is the release day it is a new way to do it. But he will get a lot of attention. If it is just the start of promoting it, people might get disappointed…
****For instance he began promoting his [[xkcd_Header_text#2015-05-14_-_New_book_Thing_Explainer|new book Thing Explainer]] in the header text. That was in May 2015 and the book was first released [https://blog.xkcd.com/2015/05/13/new-book-thing-explainer/ late November 2015]. Most of this time the header text was promoting the book.
**{{w|James Webb Space Telescope}} (JWST) going into orbit about L2 {{w|Lagrange point}}.
***Randall has already made several comics about the telescope. The latest [[2564: Sunshield]] was released just five days prior to the countdown was started.
***But the telescope will not reach the point but rather go into a large orbit around it, so a precise timer counting down to it seems a bit farfetched.
***On NASA's page on JWST it seems like it will [https://www.jwst.nasa.gov/content/webbLaunch/deploymentExplorer.html#25 go into orbit] 29.5 days after its [[December 25th Launch]], on Christmas Day, so it should have already started the orbit by the 23rd or 24th of January - 8 days before the countdown.
**{{w|Lunar New Year}}
***In China it starts on February 1st and a [https://yourcountdown.to/chinese-new-year countdown for China] is 8 hours behind.
****The South Korean time zone is UTC+9, hence 14:59 UTC = 23:59 in South Korea, one minute to Feb 1.
*****But it's weird if Randall that has basically never mentioned this holiday suddenly makes a three week countdown for it, and why choose South Korea when most would think of China in this context…?
**Randall will stop making xkcd (Goodbye in the image).
***Hopefully not.
****Agreed, {{tvtropes|PoisonOakEpilepticTrees|to be avoided}}
**[https://nationaldaycalendar.com/backward-day-january-31/ National Backward Day]
***This is not a day mentioned on Wikipedia at the time of release of the countdown, so seems unlikely.
**Maybe it will be an announcement of xkcd 2, a new and improved version for… some reason?
***Seems unlikely…
**{{w|Black History Month}}. The {{w|Greensboro sit-ins}} started on Feb 1 1960. Black History Month also begins on February 1st, also in 2022.
***But this countdown stops early on January 31st so seems unlikely.
***However, before changing the Header recently it was about [[xkcd_Header_text#2020-06-03_-_Black_Lives_Matter|Black Lives Matter]] for more than 1.5 years, first ending on December 20th 2021, less than a month before the countdown began. In between that there was a short Christmas sale reminder until a week into 2022. So it could just be another way of reminding of us the issues faced by black people in the US.
****If this was true, I feel like it would be simpler to just change back to the Black Lives Matter text at the top of the screen. Also, it seems increasingly likely as of Jan. 20th that the image is some kind of plane, which doesn't really have much to do with Black History Month (that I know of?)
**The accompanying header says specifically "xkcd updates Monday, Wednesday, and Friday"--maybe the countdown is to the reveal of a new update schedule?
***Very unlikely. This was the standard header for a long time. It was used when Randall had nothing better to say. But with all his books and the trouble in US with elections and BLM, he has used the header as a platform most of the time many years now. So the standard text is rare. But he did return it for two days before adding the count down, making it seem just like normal.
***A guess is that it returned to this, so the header text did not take any focus away from the countdown.
**[[:Category:Red Spiders|Red spider]] attack?
***Un-Likely
**He will become a father - could be a planned C-section.
***As this is unpredictable, and could go wrong, then this would be a dangerous countdown, people can be very superstitious, even if scientist.
**As it currently looks (after a [[1070: Words for Small Sets|few days]] into the countdown) it may be a trip he is taking by plane.
***Maybe going somewhere people could meet him.
****Book tour?
***Moving a long way from home (down under or the like).
****Maybe he's moving to Japan? Could be a plane, and the time zone would fit, at least.
*****Then the countdown would be until when the plane lands, not to midnight.
****What has time zones to do with this clock? It counts down to the same time all over the world, and will reach zero at the same time no matter what time zone you are in.
*****Time zones have to do with where it will be midnight when the countdown reaches zero. If it's a countdown to when January ends (a moment before February begins), then it's until that moment in the time zone where the countdown reaches zero at that time.
**Perhaps it's a start to a new series like [[1190: Time]].
***It is already a series that works like Time, so seems unlikely.
**Zero Gee flight, really looks like plane to me.
***Could be time he will first go weightless which could be fairly well known except for bad weather

==Archived Versions==
*Here is a list of the versions that has been saved to the web archive during the countdown.
**The counter in that version is written behind the date of the web archive.
**Note that the counter is active on the archived version counting minutes down from the start. Some of the versions almost changing the minutes just after loading. But it will always count from the time given here:
#[https://web.archive.org/web/20220110183238/https://xkcd.com/ 2022-01-10] 20d 20h 27m
#[https://web.archive.org/web/20220110214138/https://xkcd.com/ 2022-01-10] 20d 17h 18m
#[https://web.archive.org/web/20220111011115/https://xkcd.com/ 2022-01-11] 20d 13h 48m
#[https://web.archive.org/web/20220112005828/https://xkcd.com/ 2022-01-12] 19d 14h 1m
#[https://web.archive.org/web/20220113044552/https://xkcd.com/ 2022-01-13] 18d 10h 14m
#[https://web.archive.org/web/20220114010759/https://xkcd.com/ 2022-01-14] 17d 13h 51m
#[https://web.archive.org/web/20220114195624/https://xkcd.com/ 2022-01-14] 16d 19h 3m
#[https://web.archive.org/web/20220115052737/https://xkcd.com/ 2022-01-15] 16d 9h 32m
#[https://web.archive.org/web/20220116074923/https://xkcd.com/ 2022-01-16] 15d 7h 10m
#[https://web.archive.org/web/20220116225217/https://xkcd.com/ 2022-01-16] 14d 16h 7m
#[https://web.archive.org/web/20220118050255/https://xkcd.com/ 2022-01-18] 13d 9h 57m
#[https://web.archive.org/web/20220119213308/https://xkcd.com/ 2022-01-19] 11d 17h 26m

{{comic discussion}}

[[Category:Meta]]

2551: Debunking

2021-12-07T05:13:10Z

172.70.142.239: Transcript added

{{comic
| number = 2551
| date = December 6, 2021
| title = Debunking
| image = debunking.png
| titletext = Mark Zuckerberg has only neutral feelings toward Peppa Pig, who he understands is a fictional character, and he blames the coronavirus pandemic on other factors.
}}

==Explanation==
{{incomplete|Created by a BOT - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
This comic depicts several news headlines.

1. AP Photos show Dr.Fauci's office contains a normal number of microwaves.
2. Fact Check: Singer Billie Eilish was born years after the TWA Flight 800 Explosion.
3. Vaccinated people can remove their hats without trouble by tugging upward, say doctors.
4. Physicists say Dorito powder is affected by gravity.
5. Steering wheels will work normally on Dec 12th; Make left and right turns as usual.
6. CNN Investigation; Santa's skin is dry and healthy this year, with the same amout of oil as before.

Comment below the headline boxes says:
I don't know whether the "Don't repeat the claim in the headline debunking it" thing works or not, but it definitely makes reading the news weird.

{{comic discussion}}

2525: Air Travel Packing List

2021-10-13T03:07:56Z

172.70.142.239:

{{comic
| number = 2525
| date = October 6, 2021
| title = Air Travel Packing List
| image = air_travel_packing_list.png
| titletext = I know the etiquette is controversial, but I think it's rude when the person in front of me reclines their seat into the bell of my trumpet.
}}

==Explanation==
{{incomplete|Created by an TRUMPETBORNE PARACHUTER - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
This comic is another in a [[:Category:COVID-19|series of comics]] related to the {{w|2019–20 coronavirus outbreak|2020 pandemic}} of the {{w|coronavirus}} {{w|SARS-CoV-2}}, which causes {{w|COVID-19}}.

The comic is about a proposed air-travel packing list, and the humor stems from the fact that many people have not been flying during the pandemic, and thus they might have forgotten what to pack. So [[Randall]] is so kind as to provide a packing list with 20 items. However, apart from the first item, the rest is not something you would or even should normally bring on an airplane plane.

Many of the items are already found on passenger airplanes, some items would seem like they could be useful on a plane, while others could actually be useful in case of a plane crash (but only if you survive), while many others would be counter-productive to safe air travel, even in the event of a crash. Below in [[#Table of items|the table]] is a quick summary of each item.

The title text references the idea that there is a trumpet for each passenger provided by the airline, which is item number 16 on the list. This items also states that you, because of the COVID-19 pandemic, should remember to bring your own mouthpiece for the trumpet as a safety measure.

The trumpet idea is then combined with the common debate regarding reclining your seat in airplanes. About half of the people think that reclining is rude as it takes up the space of the person behind you. The other half think that seats recline for a reason and the person in a seat has the rights to the space behind them. See for instance this [https://www.youtube.com/watch?v=08A30v8isRs video] about such a debate. Reclining a seat has resulted in actual [https://www.independent.co.uk/news/world/americas/crime/fight-airplane-man-punch-video-b1895402.html physical fights] on board airplanes.

Here it seems that Randall sides with the anti-recliners, although maybe only in the context of the comic, because he states that reclining would prevent him from playing his trumpet, as the seat hits the bell of the trumpet. The person in front could certainly argue that playing the trumpet behind them would be very annoying, to which Randall could reply that because the trumpet is provided by the airline, he has the right to play it. This would add a new layer to the debate. This could also be Randall's way of arguing against the right to recline a seat, just because it is possible.

===Table of items===
{| class="wikitable"
! Item
! Explanation
|-
|Seat cushion
|This item is a play on sports stadium bleachers (sports stadiums were another venue commonly closed during the pandemic), because many sports fans find stadium bleachers uncomfortable and prefer to bring their own seat cushions. Airlines usually provide their own seat cushions for passengers, which are specially designed to float in water in the event of a plane crash.
|-
|{{w|Parachute}}
|Parachutes are normally used to slow down your falling out of the sky to a relatively safe speed in case of a severe problem with your aircraft, and are routinely used as a safety device by (para)glider pilots, test pilots, military aircraft crew and in similar situations when being unable to land safely is a significant concern. A parachute won't be very useful in a typical passenger airplane (even a small one) as there is no easy way to safely exit such a plane in-flight. Even the airplanes used for {{w|skydiving}} need to be specifically designed or modified for that purpose, such as having wide sliding doors that are unaffected by airflow. However, there were individual cases of people being ejected or sucked out of a passenger airplane, often during partial or complete break-up of the aircraft; in such case a parachute could arguably be useful.{{Citation needed}} Famously, [[:Category:Comics featuring D. B. Cooper|D.B. Cooper]] jumped from an airplane in flight, with a parachute but was never knowingly seen again.
|-
|Wing glue
|Probably to repair wings in the event of damage, potentially in a crash. This would be tricky (but not necessarily impossible) to apply mid-flight. This is the first of several items that are potentially useful to the flight crew or maintenance teams, but would not be useful or appropriate for passengers to bring aboard. Minor repairs (including to the wings) can be made by service personnel using {{w|speed tape}}, tape specially designed for high-speed applications. Speed tape might be mistaken for ordinary duct tape by passengers.
|-
|{{w|Air horn}}
|An air horn uses compressed air to make a very loud noise, very easily. This may be important for drawing attention to yourself in the event of a crash. Typically, emergency life-jackets on a plane are provided with a light and whistle for this purpose. The noise of an air horn might prove more effective for this purpose than a whistle, but it would become useless as soon as the compressed air ran out. Its inclusion is probably meant to suggest that the word 'air' in its name indicates that it's designed for use in an aircraft. Using one in a non-emergency situation would infuriate everyone else on the plane.
|-
|{{w|Sextant}}
|In combination with star charts, a sextant can be used to determine your position based on the location of stars in the night sky. Alternately, in combination with an accurate clock, a sextant can be used to find the position of the sun relative to the aircraft to determine the vehicle's position. In a crash, you could use this to find your way to a safe place, but sextants are rarely used, and most people are not trained on how to operate one. GPS will also allow you to find your position, is built into many phones, and is faster and easier to use than a sextant. If you've got a homing beacon, it probably makes more sense to just activate that and wait for help to arrive.

Until the early 1980s, long-range airplanes had a {{w|Air_navigation#Flight_navigator|flight navigator}} who used sextants and {{w|celestial navigation}} to determine the position of the airplane. Interestingly, it was much more accurate than early {{w|inertial navigation system}}s, and the accuracy of celestial navigation is still useful today. What made the sextant redundant was the INS' lower workload - the error accumulated by the INS during a long oceanic flight could always and easily be mitigated by other means, for example with {{w|VHF omnidirectional range|VOR}}/{{w|Non-directional beacon|NDB}} radio beacons.

A form of the sextant has also famously been used in {{w|Apollo_PGNCS#Optical_units|spacecraft navigation}} and similarly applied {{w|star tracker}}s have been used extensively to guide space-going craft ranging from suborbital missiles to interplanetary probes.
|-
|Nose plugs and goggles for pressure
|Nose plugs and goggles are commonly used in swimming but would be useless for dealing with cabin pressurization or depressurization. Since your mouth and nose are interconnected, nose plugs would be useless on their own. Trying to hold your breath in a sudden depressurization event will cause lung damage, so nose plugs wouldn't be a good thing, even if you could also seal off your mouth. Goggles would also not be useful. During depressurization, the air would just seep out. During pressurization, they would just become uncomfortable and difficult to remove.
|-
|Airplane shoes
|Airlines typically don't require the use of special footwear for passengers, nor do they provide special shoes. Before emergency egress, certain shoes (like high heels) must be discarded, though. Aircrew are also prohibited from wearing such shoes.
|-
|Navigation crystal
|Mystical form of navigation, presumably either for navigation during flight or to help you get home after a crash.
Crystals that polarize light can be used as a compass [http://www.polarization.com/viking/viking.html], but even then, their utility would be limited.
|-
|Spare batteries in case the plane runs out
|Airplanes will generally use more power than any battery small enough to be easily packed in a bag could provide. The aircraft will generally use either 115V AC at 400Hz or 28V DC, both of which are very uncommon outside of aviation. The airplane will almost never use its own batteries in-flight anyway, getting its electric power from the main engines, the APU, or, in emergencies, the ram air turbine or similar generating device. The batteries are generally only used on the ground when the engines are not running. Could be to charge a phone or similar device if the plane runs out of outlets.
|-
|{{w|Birdseed}}
|So one can attract birds. In practice, this wouldn't work for multiple reasons (high speed, altitude, and sealed windows being some of most obvious ones) and would pose a significant hazard of birds getting stuck in an engine if it did. Spreading birdseed before boarding ''could'' work to attract birds, but would be seen as misconduct by airport authorities, as attracting birds close to aircraft would pose a danger to the aircraft. Alternatively, birdseed can be used to attract birds after surviving a crash, e.g. to catch them for food.
|-
|{{w|Homing beacon}}
|Once activated, a homing beacon will send out a continuous radio signal so that rescuers can find your location. These can be very useful in a plane crash, but airplanes already carry them ({{w|Emergency position-indicating radiobeacon}}s), so you don't need to pack one yourself. Incidentally, the {{w|COSPAS-SARSAT}} system for locating distressed airplanes and ships was a cooperation started by the United States and the Soviet Union, and it was an elegant and simple solution that uses the {{w|Doppler effect}} of radio signals for accurate location - long before the {{w|Global Positioning System}}.
|-
|Meteorite antidote
|Meteorites are pieces of space rocks that make it all the way to the ground. They can cause injury but they aren't generally poisonous{{Citation needed}}, so an antidote would not help. The antidote could be an antidote to something else, possibly snakebite and be derived from meteorites but meteorites also lack verified medicinal properties.
|-
|USB wing connector
|This is a just a wire connector, but because it has wing in the name is on the list. Alternatively, the plane wings connect by USB, and this can be used to reattach wings. Airplanes usually use the {{W|ARINC 429}} protocol (or, increasingly, TCP/IP, RS427, RS232, or even CANBUS) instead of USB protocols to facilitate electronic communication between flight computers and the engines, for example.
|-
|Emergency siren
|Very much like air horn, would be useful for helping with locating you in the event of crash. It shares many of the same downsides, but would also more likely get damaged by water in case of a water landing.
|-
|Spare {{w|Flap (aeronautics)|flaps}}
|Flaps can be moved to adjust the lift/drag ratio of a wing, and are generally deployed during takeoff and landing when the aircraft's speed is slower. Flaps are very large and mounted on the wing, outside the passenger compartment, so bringing spares would be very difficult and completely useless. Flaps failing to deploy can usually be remedied by just landing at a longer runway.
|-
|{{w|Mouthpiece (brass)|Mouthpiece}} (pandemic restriction; airlines still provide the trumpet)
|A part of a brass instrument like a trumpet. Randall jokes that trumpets are provided on airplanes (which would be very obnoxious to other passengers), but due to the pandemic you cannot use a shared mouthpiece. (You shouldn't share mouthpieces for anything anyway, in general.)
|-
|Luggage ballast
|Likely to make plane more balanced. While balancing weight in a plane is indeed a real problem, it is solved by rearranging luggage and adjusting engine power slightly. Introducing ballast would mean additional weight for no real reason.
Alternatively, while a common passenger issue is to have hand- and/or hold-luggage that exceeds the airline's personal allowance, this person has ''under''weight baggage and does not wish to 'waste' the difference, so bulks it up. (Noting that someone already with the rest of the items on this list is unlikely to suffer this 'problem'.)
|-
|Flag (international flights)
|To identify your country of origin. Other flags are also used to communicate between boats without electricity, in the event the boats are in distress, so they could be used in the event of a crash.
|-
|Decoy tickets
|Maybe these would used as a distraction so you can sneak onto the plane without paying?
But also a typical trope for fictional (and real life?) attempts to evade being tracked or followed. Buy tickets for one destination, that one assumes the opposition will be fully aware of, but also arrange for another set (probably with a 'clean' identity) for your intended destination and switch to using those once in the chaos of the departure-lounge.
|-
|Keys to the plane
|Although some people pushed for it after an airplane was stolen in the {{w|2018 Horizon Air Q400 incident}}, most commercial planes do not require keys to start the engine(s) like a car does. Likewise, plane doors are not locked with a key. Instead, they are secured with a tamper seal. If a seal is found broken, the plane is thoroughly checked for any wrong-doing.
|}

==Transcript==
:[A lists of 20 items is given in two columns with 10 items in each. Each item is preceded by a checkbox. Most items only take up one line, but in the left column two items take up two and in the right one item take up three, so they take up the same space. Above is a large heading, with an explanation beneath it.]
:<big><big>Air Travel Packing List</big></big>
:<big>If you haven't flown in a while, you might not remember what you need to bring. Use this handy checklist to pack!</big>

:[Left column:]
:☐ Seat cushion
:☐ Parachute
:☐ Wing glue
:☐ Air horn
:☐ Sextant
:☐ Nose plugs and goggles for pressure
:☐ Airplane shoes
:☐ Navigation crystal
:☐ Spare batteries in case the plane runs out
:☐ Birdseed

:[Right column:]
:☐ Homing beacon
:☐ Meteorite antidote
:☐ USB wing connector
:☐ Emergency siren
:☐ Spare flaps
:☐ Mouthpiece (Pandemic restriction; airlines still provide the trumpet)
:☐ Luggage ballast
:☐ Flag (International flights)
:☐ Decoy tickets
:☐ Keys to the plane

{{comic discussion}}

[[Category:COVID-19]]
[[Category:Animals]]

Talk:2509: Useful Geometry Formulas

2021-09-07T11:00:38Z

172.70.142.239: Question re cross section

Area formulas are for 2D object as seen instead of surface of a projected 3D object. Sebastian --[[Special:Contributions/162.158.89.200|162.158.89.200]] 02:36, 31 August 2021 (UTC)

The "decorative stripes and dotted lines" are the parts of the diagrams that are intended to indicate the third dimension. The conceit of the comic is that these are superfluous. [[User:Barmar|Barmar]] ([[User talk:Barmar|talk]]) 02:56, 31 August 2021 (UTC)

;Can you "see" this as 2D?
One aspect of this comic that has not been mentioned is how strong the dashed line convention is if you are very familiar with these sorts of representations. I found it almost impossible to force my brain to see this as a 2D diagram with solid and (superflous) dashed lines. That third dimension just keeps popping out, although I could occasionally reverse the convention and see the dashed lines as in front rather than in back. [[User:Arl guy|Arl guy]] ([[User talk:Arl guy|talk]]) 14:27, 2 September 2021 (UTC)

Can someone explain how the last one works? [[User:GcGYSF(asterisk)P(vertical line)e|GcGYSF(asterisk)P(vertical line)e]] ([[User talk:GcGYSF(asterisk)P(vertical line)e|talk]]) 04:28, 31 August 2021 (UTC)

: ''bh'' is the area of the front face. The top face is a parallelogram with sides ''d'' and ''b'', with an angle of ''θ'' between them, so its area is ''d b sin(θ)''. The right face is a parallelogram with sides ''d'' and ''h'', with an angle of ''90º - θ'' between them, so its area is ''h d sin(90º - θ) = h d cos(θ)''. So the area of the whole picture is ''bh + d b sin(θ) + d h cos(θ)''.
: --[[Special:Contributions/172.68.24.165|172.68.24.165]] 04:46, 31 August 2021 (UTC)

:: In case you don't know the area of a parallelogram by heart, you can read d b sin(θ) as b * d sin(θ), where d sin(θ) is the height of the parallelogram; if you cut the right corner of the parallelogram off and add it on the left, you get a rectangle where the bottom side is b and the height is that d sin(θ), so it works out. The other parallelogram's area is h * d cos(θ), with the same reasoning. [[Special:Contributions/162.158.90.241|162.158.90.241]] 05:00, 31 August 2021 (UTC)

Funnily enough, both this comic and [[2506]] are about projection. [[User:CRLF|CRLF]] ([[User talk:CRLF|talk]]) 05:11, 31 August 2021 (UTC)

: I had considered working that into the explanation, but that needs to account for the fact that the indicated measurements (e.g. the angle θ) have to be read in 2D, not in 3D and projected. But it would be correct to say that the 2D shapes are projections of simple 3D objects. [[Special:Contributions/162.158.90.149|162.158.90.149]] 05:23, 31 August 2021 (UTC)

: Between this, [[2506]], and all the ones about Mercator and other map projections ... "projection" is a very large word in Randall's brain's word cloud. [[Special:Contributions/172.69.63.8|172.69.63.8]] 15:29, 31 August 2021 (UTC)

:: Feels to me like every comic since 2500 could be tagged "projection" in one sense of the word or another. --[[Special:Contributions/172.69.69.225|172.69.69.225]] 21:55, 31 August 2021 (UTC)

;Does the bottom-left formula have a mistake?</s>
It seems like the bottom-left formula should be ''A''=''d''(''πr''+''h'') rather than ''A''=''d''(''πr''/2+''h''), because there are two half-ellipses that add up to a complete ellipse. Am I missing something? (This doesn't ''seem'' like an extra joke, does it?) [[Special:Contributions/162.158.106.179|162.158.106.179]] 05:28, 31 August 2021 (UTC)
: No, it's correct. ''d'' is all of the major axis, not just half, so we have to divide that by ''2''. [[Special:Contributions/162.158.92.83|162.158.92.83]] 05:51, 31 August 2021 (UTC)
:: Oh, right; good call! [[Special:Contributions/162.158.106.179|162.158.106.179]] 06:49, 31 August 2021 (UTC)

;Does the top-right formula have a mistake?
I think it should be in brackets, the top triangle area needs the ''1/2'' also, so it should be: ''A''=''1/2(πab + bh)''
:No, it's correct. The bottom is a half ellipse, with area ''1/2 π a b'', and the top is a triangle with base ''2 b'' and height ''h'', so its area is ''1/2 2b h = bh''. The total area is ''1/2 π a b + b h''.
--[[Special:Contributions/172.68.25.144|172.68.25.144]] 06:49, 31 August 2021 (UTC)

;3D formulae for reference:
''4πr^2''

''πb(a+√(b^2+h^2))'' if a=b

''πr(2r+h)''

''2(bd+bh+dh)''

[[Special:Contributions/162.158.107.80|162.158.107.80]] 09:54, 31 August 2021 (UTC)
:It would be clarifying to add these to the comic, but of course they are flagrantly wrong. [[User:Baffo32|Baffo32]] ([[User talk:Baffo32|talk]]) 09:57, 31 August 2021 (UTC)
::Surely ripe for a table, in place of much of the longhand paragraph spiel (which could be kept, but simpler for just the narrative but otherwise non-technical details)... "Shape (2D)", "Area", "Pretended Shape (3D)", "Surface Area", "Volume", ¿"Notes"? (Not sure about specific Notes, some things could/should be said below the formulae/descriptions in the relevent cell to which that matters, in special cases where necessary, which might be better than a Notes either empty or jammed up with all the combined row-specific corollaries, etc, that I can imagine.) Anyway, an idea. [[Special:Contributions/141.101.76.11|141.101.76.11]] 11:56, 31 August 2021 (UTC)
:::I think the formulas are correct. Those given should be from the text book, not for those with ellipse bases. Someone has put a lot of work into giving these complicated formulas for the cone and cylinder. But I think that is overkill. I have added to the explanation the simple versions before, and would suggest deleting the complicated, which was never the intention of either text book or Randall! ;-)--[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 12:36, 31 August 2021 (UTC)
::::What complicate formulae?? --[[User:GcGYSF(asterisk)P(vertical line)e|GcGYSF(asterisk)P(vertical line)e]] ([[User talk:GcGYSF(asterisk)P(vertical line)e|talk]]) 20:28, 4 September 2021 (UTC)
: Surface area. Not volume. My bad. I usually consider volume associated with pics like like that. Don't use surface area much. [[User:Baffo32|Baffo32]] ([[User talk:Baffo32|talk]]) 22:22, 1 September 2021 (UTC)

add an extra edited image that is the comic without dotted lines to make it easier to see the 2d shapes? [[Special:Contributions/172.69.71.177|172.69.71.177]] 12:46, 31 August 2021 (UTC)Bampf
:And an animated GIF of the 3D solid objects rotating to show their real shapes. At different speeds. If you have the time. :-) Robert Carnegie rja.carnegie@gmail.com [[Special:Contributions/141.101.76.11|141.101.76.11]] 16:31, 31 August 2021 (UTC)
: Image here: https://i.imgur.com/dq7VmnK.png Editing done myself, feel free to upload it to this wiki if you have an account on this wiki. :) --[[Special:Contributions/162.158.88.29|162.158.88.29]] 17:22, 1 September 2021 (UTC)

Please do check my (additional) changes to the bottom-right item (hexagon-cum-prism) in both main and transcript texts. As hinted in my edit notes, cos-theta is important because the skewed tetrahedron (rhomboid, whether in plan or the true area of the 'fake' perspective) is not d*b in area. The fact that without the theta it would look like a standard oblique orthographic projection with entirely right-angled corners is perhaps part of the (intended?) confusion, although we can probably assume that all unmarked (and, of course, uncongruent/uncomplimentary) angles are 90° so that it isn't a full on parallelepiped with an additional phi-angle on an adjacent face and a complicated third dependent-angle somewhere upon the remaining face-plane. As such, I put in the cosine element to both the 3d surface formula (it only affects the bd-shape, the both of them) and the 3d volume (from this shape, extrudes without further adjustment straight up the h-axis), but I ''always'' have to second guess if I've done this simple bit of trig right, it seems, even though I should know better and just trust to SOHCAHTOA... ;) [[Special:Contributions/162.158.158.146|162.158.158.146]] 13:24, 31 August 2021 (UTC)
:(Case in point: I thought I'd added cosines, and I'd put sines ''anyway'', when fussing about copying the clipboarded theta-character into the right place! Re-read, seen, corrected(?) this myself. Unless I thought I was was wrong; but I was wrong, I was right!) [[Special:Contributions/162.158.155.145|162.158.155.145]] 13:33, 31 August 2021 (UTC)

I believe both of those prism formulas should use sine theta. If theta is ninety degrees, then sine theta will be 1 (thus reducing to the rectangular case), whereas cosine of 90 degrees is zero.[[User:Tovodeverett|Tovodeverett]] ([[User talk:Tovodeverett|talk]]) 15:19, 31 August 2021 (UTC)
:You're right (me again, from just above), I was rushed and ''had'' been right first time, I realised while I was off-grid and it was nagging away at the back of my head. I'm better on paper (or when I can sanity-test real code, but for some reason tapping it in like this just screws my mind up, taking away/inverting my technical ability and reason. (I blame the microwaves emitting from my tablet... pass the tinfoil hat!) [[Special:Contributions/162.158.158.178|162.158.158.178]] 16:29, 31 August 2021 (UTC)

Unconvinced by the cone! The equation shown, is correct for an isosceles triangle with a half-ellipse on its base. But that shape has 'corners' where the sides meet that half-ellipse. In a 3D projected view of an actual cone, the sides will meet the base ellipse at a tangent, meaning that it is more than a half-ellipse. But I suppose it's close enough as an approximation...[[Special:Contributions/172.69.55.131|172.69.55.131]] 15:57, 1 September 2021 (UTC)
: I verified your claim by imagining the surface of the cone as formed by a set of lines extending from the different points on the ellipse to a single fixed point at the tip. No matter where you put that tip point, the outermost lines seem tangent to the ellipse. Seems it works for both perspective and orthographic projections. Updated the explanation. Randall's formula is incorrect, especially for very short cone projections. [[User:Baffo32|Baffo32]] ([[User talk:Baffo32|talk]]) 22:46, 1 September 2021 (UTC)

:: I expanded the text slightly, and worked out the correct formula: it should be (2π - 2arctan(h/a))ab + b sqrt(h^2 - a^2). Can someone verify that, format it properly for the wiki, and add it? The easy way to check it is to shrink the diagram horizontally so the ellipse is a circle of radius a. (Does the wiki not have MathJax or similar installed? Seems odd, given Randall Munroe's interests.) It's maybe also worth mentioning that looking closely at the picture at a pixel level shows that he did draw the tangents, rather than do the half-ellipse + triangle that the formula suggests. --[[Special:Contributions/172.69.90.75|172.69.90.75]] 16:48, 2 September 2021 (UTC)

; It's 3am (okay 5am) and I made it really long!

I just followed the directions in the "incomplete" which said to add in explanations of the formulae ... Please feel free to edit to take out redundancy. However I did add in the following explanations:
- the fact that the formula in the third figure is actually the same as the cross-section represented by the ellipse, which is why you may not get the joke after reading the first picture;
- the use of 'd', 'r' and 'h' in the third figure, which adds to the confusion as they imply "diameter", "radius" and "height"
- the fact that the area calculations must take into account the overlapping shapes (there were previously references to "semi-ellipses" which are extrapolations, not what's drawn there)
Haven't yet done the last figure
- pretty sure 'b' 'd' and 'h' are for 'breadth', 'depth' and 'height' and while 'height' is also used for 2D rectangles, 'breadth' less so in maths textbooks (usually 'width')
- whoever pointed out that there is a theta as well, pretty sure it's only there because it's necessary for the area calculation, as 'depth' only really applies as labelled to rectangular prisms - if the base were not rectangular, 'd' would not be equal to the 'depth'
Will try to come back later and shorten... [[Special:Contributions/162.158.166.40|162.158.166.40]] 18:56, 1 September 2021 (UTC)

Someone [https://www.explainxkcd.com/wiki/index.php?title=2509:_Useful_Geometry_Formulas&diff=217438&oldid=217434 thought that] "formulae" was a typo for "formulas" (which it might easily be, on a QWERTY or similar layout). Not going to revert, but note that (for a mathematical formula, if perhaps not a chemical one/etc, but there's plenty of mixed use) this is actually quite correct. If it were up to me alone (I didn't write that one, orother mentions like in the above Talk contribution), for the record, I'd probably have used "formulæ" myself. ;) [[Special:Contributions/162.158.155.145|162.158.155.145]] 20:28, 1 September 2021 (UTC)

If you don't assume that the bottom right figure is 3D, what's the justification for projecting upward and assuming that the angle theta is also the angle of the top parallelogram? [[User:Arl guy|Arl guy]] ([[User talk:Arl guy|talk]]) 02:25, 2 September 2021 (UTC)
:If you assume that the two rectangles have equal width and height, then it can be mathematically proven that the angles must be equal (probably using congruent triangles). However this assumption is not stated on the figure. That said, you would make the same assumption for the 3D figure, along with a whole bunch of other assumptions of course.[[Special:Contributions/172.70.147.23|172.70.147.23]] 06:31, 2 September 2021 (UTC) Edit: The two rectangles must have equal width and height to make the rest of the shapes parallelograms in the first place. If they aren't identical you get trapezoids all round and possibly a bunch of different angles. [[Special:Contributions/172.70.143.22|172.70.143.22]] 06:43, 2 September 2021 (UTC)
:Yes, I think you are mostly right, but you don't necessarily get trapezoids all around. You can move the top solid line down and to the right and rotate the top left and top right slanted lines to keep the top shape a parallelogram, but the right shape will now be a trapezoid. I think the key assumption is that all the solid and dashed lines that loop parallel are, in fact, parallel. [[User:Arl guy|Arl guy]] ([[User talk:Arl guy|talk]]) 14:20, 2 September 2021 (UTC)
:There's always many possible {{w|Ames room|unindicated perspective tricks}} (or axonometric/othographic ones, as might be more appropriate) in which the components of lines and relationships towards/away from the viewer are non-zero (or {{w|Penrose triangle|not non-zero in the way expected}}). Various of the shapes involved could be infinitely warped with leans, curves or even highly inflected wiggles to allow ''some'' 'as expected' profile even as others that should be connected are not. (Though it would make the surface 'planes' warped and distorted, even more against the conventions of wireframe diagrams.)
:Because of dependencies, as the theta moves the other similar angles ''might'' be thetas too, or they could be kept as RAs and (?)three ''other'' chosen angles could be distorted (in or out of the page, by a calculable and entirely derivative amount) to compensate. Or, like the Triangle illusion, there's overlaid duplicate edges with not all/any vertices actually being the same, just in the same illustrated place. (Again, making a mockery of the 'simple' diagram, but we're already way past that. ;) ) [[Special:Contributions/162.158.155.247|162.158.155.247]] 08:56, 2 September 2021 (UTC)
::Sure, but we were talking about the 2D figure and taking it at "face" value - the internal angle is defined while the ones you'd actually use for the parallelogram area calculations aren't, and neither are the dimensions of the upper rectangle. In a proper geometric figure you'd have markings showing which lengths are equal and which angles are right angles.[[Special:Contributions/172.70.143.22|172.70.143.22]] 05:38, 3 September 2021 (UTC)

'''Subtext??:''' I wonder if this comic implies that we are being transformed from 3d creatures into 2D creatures...
hadaso --[[Special:Contributions/162.158.91.184|162.158.91.184]] 07:04, 5 September 2021 (UTC)

'''Cross-section - reword please''' I made a wording error in describing all points on the "cross-section" of the sphere as being equidistant from the centre, and I'm stuck on how to fix it concisely. Problem is that "cross-section" is ambiguous - I think mathematically it ''could'' mean the circle at the intersection of the hollow sphere and the plane, but to me it usually means the part of the plane where it intersects the solid sphere, which makes the statement false. I want to replace it with "circle", with the quote marks, but we're actually talking about the ellipse-cum-circle so I'm not sure if that's good enough. [[Special:Contributions/172.70.142.239|172.70.142.239]] 11:00, 7 September 2021 (UTC)

Talk:1757: November 2016

2021-09-06T08:13:17Z

172.70.142.239:

Ok transcript hopefully complete, but please check it over, as I did it while tired and staying up late waiting for the election results. [[User:Wyrme|Wyrme]] ([[User talk:Wyrme|talk]]) 05:43, 9 November 2016 (UTC)

: Spoiler alert: Trump won. --[[User:JayRulesXKCD|JayRulesXKCD]] ([[User talk:JayRulesXKCD|talk]]) 16:16, 9 November 2016 (UTC)

The main idea of the comic is stated in the first sentences "If they're [age], you say: "Did you know [thing] has been around for the majority of your life?"
The majority of your life means "more than half your life". For each of the age stated in the comic, something that happened more than half the age ago is stated.
As an example for the first two:
Grand Theft Auto IV was released in 2008, which is 8 years ago. More than 8 years is at the same time more than half of 16 years, which means "the majority of a 16 year old's life"
The next one goes for Rickrolling, which is "a prank and an Internet meme involving an unexpected appearance of the music video for the 1987 Rick Astley song 'Never Gonna Give You Up'. The meme is a type of bait and switch using a disguised hyperlink." according to [https://en.wikipedia.org/wiki/Rickrolling wikipedia]. Even if the first reference is from 2007, the same Wiki page says that 'By May 2008, the practice had spread beyond 4chan and became an Internet phenomenon'. May 2008 is more than 8 and a half years ago which is more than half of 17 years.
It goes on and on, with "Aqua Teen Hunger Force Colon Movie Film for Theaters" which is a 2007 American Flash animated surreal comedy film", which again is more than 9 years ago and so on.
Sorry if I'm not clear enough but I hope you got it.
[[User:Anarhistu|Anarhistu]] ([[User talk:Anarhistu|talk]]) 11:19, 9 November 2016 (UTC)

: Yeah, the "majority part" is a bit confusing. I looked up 35 and saw "The Matrix" and I was like "wait, that didn't come out 35 years ago?!". Well, it didn't and that's not what the comic implys. However, it has been around for a MAJORITY (= more than half) of my life. [[Special:Contributions/162.158.202.141|162.158.202.141]] 12:37, 9 November 2016 (UTC)

I'm only 32, but saddened at the entry for 40. C&H was (and still is) one of my favorites. I say we all just take off today and play some Calvinball. Who's with me? [[Special:Contributions/162.158.69.100|162.158.69.100]] 12:48, 9 November 2016 (UTC)

There is this last thing "over 41, we don't care" which I cannot really explain. Maybe the 40+ year olds seen all of these later in their life but why stop at this point? (which is around 1996, according to the "rules")? The internet has been around since way before that and if we take the first popular browser this was about 1993 or so. That would take us to 46. Is there any specific event which might be a reason to stop at 41? [[User:Anarhistu|Anarhistu]] ([[User talk:Anarhistu|talk]]) 13:12, 9 November 2016 (UTC)
: No, people above 40 already feel old, no need for a chart --[[Special:Contributions/162.158.88.204|162.158.88.204]] 13:18, 9 November 2016 (UTC)
::Jurassic Park, Mrs. Doubtfire, Robin Hood Men In Tights [[Special:Contributions/162.158.69.100|162.158.69.100]] 13:21, 9 November 2016 (UTC)
:::He has previously stopped at a given age and stated that anyone older should feel old already --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 20:43, 9 November 2016 (UTC)

But if I look in x years, then the entry at current age + x will have been there for (current age +x)/2 + x years, so if I look at it again after my age has doubled, the thing has been there for my entire life.
--[[Special:Contributions/162.158.88.204|162.158.88.204]] 13:17, 9 November 2016 (UTC)
:Sorry your are completely wrong. If you are 20 now and look at something happening 10 years ago. Then when you are twice as old (40) you look at the same ting and that will then be 30 years old. It will always be 10 years younger than you. There was a mistaken explanation of the title text saying something like what you say, and now I have corrected it. He just means that if you show them this chart again when their age has doubles, you can say that this chart has now existed in the majority of your life. --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 20:43, 9 November 2016 (UTC)

Heh. Randall isn't always prompt in posting new comics early on M/W/F, but this one went up promptly at 12:01am. He deserves to be embarrassed after the communist comic he posted on Monday. [[Special:Contributions/172.68.55.83|172.68.55.83]] 13:31, 9 November 2016 (UTC)
:How the hell did you make out Clinton to be a communist? It's Trump who likes Putin, where Clinton would be more against him... I guess he just thought people needed something that could distract them from the election, since most of his readers (especially after his previous comic) would have rooted for Clinton because of their fear that Trump won. On the other hand most people probably feels old today, after the election, so in that way the comic is a bit of a waste... --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 20:43, 9 November 2016 (UTC)
::Sorry, but we Americans disagree with you. Too bad, so sad. {{unsigned ip|172.68.55.83}}
::: Actually, we Americans chose Clinton, probably by a margin of >1M votes once CA and OR finish counting. [[User:Miamiclay|Miamiclay]] ([[User talk:Miamiclay|talk]]) 22:40, 11 November 2016 (UTC)
::::Almost three million, as it turned out; the margin in the popular vote was greater than the entire population of Chicago. [[User:Whoop whoop pull up|Whoop whoop pull up]] ([[User talk:Whoop whoop pull up|talk]]) 18:04, 4 January 2018 (UTC)

I don't understand how this is supposed to work. If I wanted to make someone feel old, I would pick an event that they think is fairly ancient and tell them: "do you realize you're *more* than twice as old as this?" Here, Randall does the opposite, he says: "did you know you're *less* than twice as old as this", so what? E.g. "Twitter has been around for a majority of your life" is true of anyone who is 0 to 20, so how is it supposed to make a 20-year-old feel old? Did Randall get his comic backwards or am I missing something?
Zetfr 14:26, 9 November 2016 (UTC)
:The idea is that you don't pick events that they think are ancient, you pick events that they think are recent. [[Special:Contributions/162.158.222.138|162.158.222.138]] 16:46, 9 November 2016 (UTC)

The explanation says "The titletext points out that the same chart can be used for the same person much later in their life. However, the major event shifts earlier and earlier into their life; when their age has doubled, the event in the chart has happend in the year of their birth." This makes no mathematical sense - the major event would shift earlier ''into their life'', but not ''in time'', and would remain the same distance from their birth year. What is probably intended is that now ''the chart itself'' will be around for a majority of their life (though I agree with the above commenter that it would probably make one feel young, not old). --[[Special:Contributions/172.68.10.90|172.68.10.90]] 14:54, 9 November 2016 (UTC)
:Exactly, what I wrote above to the other comment on this, and I have tried to correct it in the explanation. --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 20:43, 9 November 2016 (UTC)

I fixed the rest of the blank explanations, such as Gmail, Nintendo Wii, and others. Please fill in the 'Aqua Teen Hunger Force', as I was not able to find information about it anywhere and I have not seen that show, nor the movie itself, so I cannot answer. --[[User:JayRulesXKCD|JayRulesXKCD]] ([[User talk:JayRulesXKCD|talk]]) 15:14, 9 November 2016 (UTC)

Actually Randall may be wrong with some of those entries at the current moment. Let's say that somebody is 19 years old, but their 20th birthday is on the 10th of November. The entry for their age is the Nintendo Wii which came 9 years, 11 months and 20 days ago (as of November 9), which is not more than half of the subject's age. I think this occurs on quite a few of those entries, so either the chart is intended to be addressed only to people during their birthdays, or one can make fun of any geek who parades this list for not being rigorous with their maths. [[Special:Contributions/108.162.246.35|108.162.246.35]] 15:38, 9 November 2016 (UTC)
: That's pretty pedantic. We're so close to the end of the year that we can reasonably assume it means "people who turned X years old in 2016" [[Special:Contributions/141.101.98.165|141.101.98.165]]
::I think he just goes for events that is approximately half as old as the person. Only error he seems to have made is with the Matrix, which came when the 35 years old of today was 18, and it has thus only been in their life about 17 years. --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 20:43, 9 November 2016 (UTC)
:Pedantic? This is xkcd we're talking about. Not only that there's a post commenting on this comic's timing regarding the MWF pattern, as on every other similar comic, a fact that should be taken even less seriously, but Randall has greatly shown his support of pedants partly by repeatedly depicting them as empowered in his comics. I think that pedants have to either take responsibility for their demeanour or admit to the fact that their peculiarity does not even have the tradeoff of accuracy it should have. In other words, anyone who bothers others with a list like this better have precise information to offer if they expect to have any reason not to waste others' time. [[Special:Contributions/108.162.246.35|108.162.246.35]] 05:25, 10 November 2016 (UTC)

36 years old: Half-life has been around half of your life.
18000 years old: Half of the curium-250 atoms have been around half of your life. [[Special:Contributions/108.162.219.82|108.162.219.82]] 17:58, 9 November 2016 (UTC)

You might be old if you remember watching the Berlin Wall being torn down on television.
You would be even older if you remember reading about the Berlin Wall at the time it was being built.
I remember both ... I read about the wall being built in elementary (primary) school current events. [[User:Rtanenbaum|Rtanenbaum]] ([[User talk:Rtanenbaum|talk]]) 21:30, 9 November 2016 (UTC)
:Interesting, but not strange, to bring that wall up today. Since it is today the anniversary for it's destruction in 1989 (17 years ago so would have been good for the 34 years old). And very ironic that a man is then elected on this very day who has promised to build and even bigger wall between his country and another. --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 22:14, 9 November 2016 (UTC)
: If you want to feel really old, just remember that The Hoff sang "Looking for Freedom" in front of the Berlin Wall. ;) [[Special:Contributions/198.41.242.242|198.41.242.242]] 11:01, 10 November 2016 (UTC)
: Correction, 1989 is 27 years ago, half the life of a 54 year-old [[User:Rtanenbaum|Rtanenbaum]] ([[User talk:Rtanenbaum|talk]]) 15:02, 10 November 2016 (UTC)
:::Speaking of 1989, Taylor Swift's musical debut would be a viable alternative to the Wii RTM. [[User:Whoop whoop pull up|Whoop whoop pull up]] ([[User talk:Whoop whoop pull up|talk]]) 18:04, 4 January 2018 (UTC)
::Auch I feel old now, that I could make such a mistake. Thanks for correcting it. But at least I'm not 54 yet, but I do remember the day very well. Just happy Randall raised the bar since his movie ages, so my age is still on the list and so I'm not just in the "rest above 41 group" ;-) --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 15:06, 10 November 2016 (UTC)
::: It happened to me. Twice now, thanks to this comic. The first time was in grad school, when I was a student over the traditional age, Another student put out a survey which asked age at the end, offering various check boxes where I had to check the last one. I howled, "The next box is a pine box!" [[User:Ke4roh|Ke4roh]] ([[User talk:Ke4roh|talk]]) 18:46, 16 November 2016 (UTC)

Randall seems to be confused. If you think Twitter is young, then finding out that it's existed for a majority of your life would make you feel young. If you think Twitter is old, then of course it's been around for a majority of your life, it's old.

The right one would be: such-and-such has been around for less than 50% of your life.[[Special:Contributions/141.101.98.112|141.101.98.112]] 15:52, 3 April 2020 (UTC)

Grand Theft Auto IV was merely "popular"?
It set the record for highest first-day earnings across all media types until The Dark Knight was released that summer.
Fun fact: The Dark Knight was added to the National Film Registry last year (2020), along with Shrek. As of that year, there are six 2000s theatrically-released movies on the registry (Memento, Shrek, Real Women Have Curves, Brokeback Mountain, The Dark Knight, and The Hurt Locker).

2509: Useful Geometry Formulas

2021-09-02T07:10:32Z

172.70.142.239:

{{comic
| number = 2509
| date = August 30, 2021
| title = Useful Geometry Formulas
| image = useful_geometry_formulas.png
| titletext = Geometry textbooks always try to trick you by adding decorative stripes and dotted lines.
}}

==Explanation==
{{incomplete|Created by a STRIPED AND DOTTED TEXTBOOK ILLUSTRATOR. Explain the formulas for each of the areas, and also the correct formula for the 3D object they seems to represent. Do NOT delete this tag too soon.}}
This comic showcases area formulas for the areas of four two-dimensional geometric shapes which each have extra dotted and/or solid lines making them look like illustrations for 3-dimensional objects. The first, a simple equation for the area of a circle, the second an equation for the area of a triangle with a semi-elliptic base, the third an equation for the area of a rectangle with an elliptical base and top, and the fourth and equation for the area of a hexagon consisting of two opposing right angled corners and two parallel diagonal lines connecting their sides. In each case, only the area formed by the outline of each shape is calculated.

Similar illustrations are commonly found in geometry textbooks, which are used to depict three-dimensional figures on a two-dimensional page. They commonly make use of slanted lines to indicate edges receding into the distance, and dashed lines to indicate an edge occluded by nearer parts of the solid. The joke is that the formulae given here are for the area of each two-dimensional shape within its outer solid lines, not for the surface area or volume of the illustrated 3D object (as would be shown in the geometry textbook). The title text continues the joke by claiming that the dotted lines are simply decorative.

The illustrations depict the following plane or solid figures, depending on the interpretation.

; Top Left - Circle with inscribed ellipse, or Sphere
This illustration is commonly used to depict a three-dimensional sphere, with the ellipse representing a "horizontal" or axial cross-section through the centre; the solid lower half of the ellipse represents the "front" of the circumference of this cross-section, while the dotted upper half represents the "back" of the same section, which would be occluded from view if this were a solid shape.

The radius of the circle, from the centre to the right edge where it meets the ellipse, is labelled 'r'. In a textbook diagram of a sphere the radius may be instead labelled with a diagonal line from the centre to a different point on the ellipse, implying the generality that all points on that cross section, and indeed on the whole spherical surface, are at the same radius from the centre. However this line would be shorter on the page than the actual radius, making it useless for the formula of the area of the 2D outer shape.

The area of the 2D shape on the page is the area of the circle, which is A = πr2. This is captioned below the figure.

Coincidentally the area of the horizontal cross-section of the 3D sphere, as depicted by the ellipse, is also πr2, and a reader familiar with such diagrams might initially assume that this is what was meant. However this does not extend to the other figures.

The 3D sphere commonly depicted by this drawing would have a volume of 4/3 πr3 and a surface area of 4πr2.

; Top Right - Ellipse with symmetrical diagonal lines, or Cone
This illustration is commonly used to depict a three-dimensional right circular cone, with the lower half of the ellipse representing the "front edge" of the bottom surface, and the upper half representing the occluded "back edge". However such drawings would usually not use both 'a' and 'b' to describe the radius of the base of the cone, which is drawn as an ellipse due to foreshortening. Alternatively, the drawing could depict a right elliptical cone.

Randall approximates the area of the 2D shape on the page as the sum of the area of the triangle formed by the major axis of the ellipse and the two lines, and half of the area of the ellipse (π/2 ab), since most of the upper half of the ellipse overlaps the triangle. The equation for this area is A = 1/2 πab + bh. This is captioned below the figure.

The actual area of a picture of a cone is not quite Randall's approximation, because the sides connect at the points on the ellipse where they can spread widest and form tangents to the ellipse, and such points are a little higher than those which define the major axis.

The 3D right circular cone commonly depicted by this drawing would have a volume of πr2h/3 where r=a=b. The area of the "lower" surface would be πr2, while the surface area of the upper conical surface would be πr√(h2 + r2). Neither of these areas correspond with the caption in the comic, nor does the total surface area (the sum of these two).

If we do not assume that a = b, this drawing could also depict a right elliptic cone. The volume of the elliptic cone would be π/3 abh. The area of the lower surface would be πab and the area of the curved upper surface would be 2a√(b2 + h2) ∫01 √(a²h²(t²-1) - b²(a²+h²t²)/a²(t²-1)(b²+h²)) dt.

; Bottom Left - Two ellipses joined vertically, or Cylinder
This illustration is commonly used to depict a 3D cylinder, or right circular prism. In this case, the upper ellipse represents the "visible" part of the top circular surface, with its "depth" shorter than its "width" due to perspective, and the lower part of the lower ellipse represents the "front" edge of the lower surface; the dotted half of the lower ellipse represents the occluded "back" edge of the lower surface.

To add to the confusion, the upper ellipse has its major axis labelled 'd' which usually denotes the diameter of a circular surface, while the lower ellipse has its semimajor axis labelled 'r' which similarly denotes a radius, even though the ellipses drawn have neither diameter nor radius. The 'h' denoting height is also used for both rectangles and solid objects. While 'd' in this case is required for the area calculation of the 2D shape, in textbooks only 'r' may be marked and the arrow may be offset at a diagonal rather than vertical.

The non-overlapping parts of the 2D shape are composed of the rectangle formed by the major axes of the two ellipses and the vertical lines, plus half of the top ellipse and half of the bottom ellipse. The area of the rectangle is dh, and the area of an ellipse with semimajor axis d/2 and semiminor axis r is πrd/2. The total area is A = d(πr/2 + h), which is captioned below the figure.

A 3D right circular prism (cylinder) would have a volume of πr2h and a surface area of 2πr2 + πdh, or 2πr(r + h) since in this case d = 2r. The area of each flat surface would be πr2. If we do not assume d = 2r, then the lateral surface area of the right elliptic cylinder is 4h ∫01 √(1 - t²(1-4r²/d²)/1 - t²) dt. The volume is π/2 rdh.

; Bottom Right - Parallel Hexagon, or Prism
This illustration is commonly used to depict a rectangular prism, with 'b' denoting the 'breadth', 'd' the 'depth' and 'h' the 'height'. However the labelled angle θ, which is necessary for the area calculation of the 2D shape, would not normally be used in a diagram of a rectangular prism, as all angles are assumed to be right angles. A rhomboidal prism could be accurately described by this diagram with the assumption that the 'base' parallellogram is perpendicular to the 'front' and that the only non-right angle is θ. In that case 'd' would not accurately describe the depth of the solid, which would actually be d sin θ.

The area of the 2D shape is comprised of the rectangle at lower left, the parallellogram above it and the parallellogram on the right. The area of the rectangle representing the front face of the prism is bh. The area of the upper parallelogram is db sin θ. The area of the right parallelogram is dh cos θ. The equation for this area is A = bh + d(b sinθ + h cosθ) as is given below the figure.

The surface area of the prism would be 2bh + 2db sin θ + 2dh. The volume is bdh sin θ. Assuming a 3D shape, θ can be artificially altered by the projection; the assumption could be made that θ is 90 degrees, and sin θ is 1 (and therefore can be eliminated from the formulas), but since θ is marked, such an assumption might not be valid.

In the history of the development of computer-generated 3D graphics, calculations of the apparent visual area taken up by the projection of a volume may have been useful in occlusion-like optimizations, where each drawn pixel may be passed through many fragment shaders.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[Four figures in two rows of two, each being a common two-dimensional representation of a three-dimensional object, with solid lines in front and dotted lines behind. Each figure has some labeled dimensions represented with arrows and a formula underneath indicating its area. Above the four figures is a header:]
:Useful geometry formulas

:[Top left; A circle with an inscribed concentric ellipse sharing its horizontal diameter. The edge of the ellipse above the major axis is drawn with a dotted line, while the lower edge is drawn with a solid line, similar to textbook depictions of a 3D sphere. The shared radius/semi-major axis to the right of the centre is drawn as an arrow and labelled 'r'. ]
:A = πr²

:[Top right; An ellipse with horizontal major axis, plus two straight lines: one from each end of the major axis, up to a point vertical to the centre of the ellipse, so that the major axis of the ellipse (not drawn) and the two lines would form an isosceles triangle with a vertical axis of symmetry. The upper edge of the ellipse above the major axis is drawn with a dotted line, while the lower edge is drawn with a solid line, similar to textbook depictions of a right elliptical cone, or more commonly a right circular cone. The semi-minor axis of the ellipse is drawn with an arrow down from the centre and labelled 'a' and the semi-major axis is similarly drawn to the right of the centre and labelled 'b'. To the right of the shape, the height of the isosceles triangle is drawn using arrows, and labelled 'h'.]
:A = 1/2 πab + bh

:[Bottom left; Two ellipses of the same dimensions, with major axes horizontal, drawn vertically one above the other, with vertical lines connecting each end of the major axis of the top ellipse to the corresponding points on the bottom ellipse. The upper edge of the bottom ellipse above the major axis is drawn with a dotted line, while the lower edge is drawn with a solid line, similar to textbook depictions of a right elliptical prism or, more commonly, a right cylinder (circular prism). Inside the shape, the major axis of the upper ellipse is drawn as a double-ended arrow and labelled 'd'. The semi-minor axis of the lower ellipse is drawn as an arrow down from the centre and labelled 'r'. To the right of the shape, the length of the vertical lines is replicated using arrows, and labelled 'h'. ]
:A = d(πr/2 + h)

:[Bottom right; Two rectangles of the same vertical and horizontal dimensions, drawn with one offset diagonally to the upper right of the other, with diagonal lines connecting the corresponding vertices, forming a hexagon with opposite sides parallel. The upper right rectangle has its left and bottom sides drawn with dotted lines, and a similar dotted line is used connecting the bottom left corner of the two rectangles, similar to textbook depictions of rhomboid-based right prisms, or more commonly rectangular prisms. Outside the shape, the bottom edge of the lower rectangle is redrawn below the shape with arrows and labelled 'b'. The length of the left edge is similarly redrawn to the left and labelled 'h'. The length of the diagonal line connecting the upper left corners of the two rectangles is similary redrawn on the top left using arrows and labelled 'd'. The acute angle between the bottom edge of the lower rectangle, and the dotted diagonal connecting the two lower left corners, is labelled 'θ']
:A = bh + d(b sinθ + h cosθ)

{{comic discussion}}

[[Category:Math]]

2509: Useful Geometry Formulas

2021-09-01T18:17:11Z

172.70.142.239: /* Explanation */ Third shape

{{comic
| number = 2509
| date = August 30, 2021
| title = Useful Geometry Formulas
| image = useful_geometry_formulas.png
| titletext = Geometry textbooks always try to trick you by adding decorative stripes and dotted lines.
}}

==Explanation==
{{incomplete|Created by a STRIPED AND DOTTED TEXTBOOK ILLUSTRATOR. Explain the formulas for each of the areas, and also the correct formula for the 3D object they seems to represent. Do NOT delete this tag too soon.}}
This comic showcases area formulas for four two-dimensional geometric shapes which each have extra dotted and/or solid lines making them look like illustrations for 3-dimensional objects - the first, a simple equation for a circle, the second an equation for a triangle with a semi-elliptic base, the third an equation for a rectangle with an elliptical base and top, and the fourth a hexagon consisting of two opposing right angled corners and two parallel diagonal lines connecting their sides. In each case, only the area formed by the outline of each shape is measured.

Such illustrations are commonly found in geometry textbooks, which need to depict three-dimensional figures on a two-dimensional page. They commonly make use of slanted lines to indicate edges receding into the distance, and dashed lines to indicate an edge occluded by nearer parts of the solid. The joke is that the formulae given here are for the area of each two-dimensional shape within its outer solid lines, not for the surface area or volume of the illustrated 3D object (as would be shown in the geometry textbook). The title text continues the joke by claiming that the dotted lines are simply decorative.

The illustrations depict the following plane or solid figures, depending on the interpretation.

; Top Left: Circle, or Sphere
A circle with radius r, with a concentric ellipse drawn inside it, sharing its horizontal diameter. The lower half of the ellipse is drawn with a solid line and the upper half with a dotted line. This illustration is commonly used to depict a three-dimensional sphere, with the ellipse representing a "horizontal" or axial cross-section through the centre; the solid lower half of the ellipse represents the "front" of the circumference of this cross-section, while the dotted upper half represents the "back" of the same section, which would be occluded from view if this were a solid shape.

The area of the 2D shape on the page is the area of the circle, which is A = πr2. This is captioned below the figure.

The 3D sphere commonly depicted by this drawing would have a volume of 4/3 πr3 and a surface area of 4πr2. The vertical cross-sectional area of the sphere and the horizontal cross-sectional area would both be the same as the area of the 2D shape on the page, πr2. In textbooks a drawing of a sphere such as this may be captioned with its volume, surface area or the area of the horizontal cross-section depicted by the ellipse, so that at first glance a reader familiar with such images may assume that the caption in the comic is meant to show the formula for the horizontal cross-section. This is not the case for the rest of the figures.

; Top Right: Ellipse Overlapping Isosceles Triangle, or Cone
An isosceles triangle with a vertical axis of symmetry, of height 'h', with its base replaced by an ellipse with semi-minor axis 'a' (vertical) and semi-major axis 'b'. The lower half of the ellipse forms the outline of the combined shape, while the upper half of the ellipse is depicted with a dotted line. This illustration is commonly used to depict a three-dimensional right circular cone, with the lower half of the ellipse representing the "front" of the bottom surface, and the upper half representing the occluded "back" edge; the drawing may also depict a right elliptic cone. In textbook depictions of a right circular cone, 'a' is assumed to be actually equal to 'b', but because it represents the dimension "depth" which cannot be drawn on the page, it is instead drawn as shorter than "b" due to parallax.

The area of the 2D shape on the page is the sum of the area of the triangle (bh), and half of the area of the ellipse (π/2 ab), since most of the upper half of the ellipse overlaps the triangle on the page. The equation for this area is A = 1/2 πab + bh. This is captioned below the figure.

The 3D right circular cone commonly depicted by this drawing would have a volume of πr^2*h/3 where r=a=b. The area of the "lower" surface would be πr2, while the surface area of the upper conical surface would be πr√(h2 + r2). Neither of these areas correspond with the caption in the comic, nor does the total surface area (the sum of these two).

If we do not assume that a = b, this drawing could also depict a right elliptic cone. The volume of the elliptic cone would be π/3 abh. The area of the lower surface would be πab and the area of the curved upper surface would be 2a√(b2 + h2) ∫01 √(a²h²(t²-1) - b²(a²+h²t²)/a²(t²-1)(b²+h²)) dt.

; Bottom Left: Two Ellipses Overlapping Rectangle, or Cylinder
Two ellipses with major axis 'd' and semiminor axis 'r', with vertical lines between the corresponding ends of the major axes of each, so that the vertical lines and the major axes would form a rectangle of height 'h'. The upper half of the upper ellipse, the lower half of the lower ellipse and the vertical lines form the outline of the combined shape. The upper half of the lower ellipse is drawn with a dotted line, while the lower half of the upper ellipse is drawn as a solid line. This illustration is commonly used to depict a 3D cylinder, or right circular prism. In this case, the upper ellipse represents the "visible" part of the top circular surface, with its "depth" shorter than its "width" due to parallax, and the lower part of the lower ellipse represents the "front" edge of the lower surface; the dotted half of the lower ellipse represents the occluded "back" edge of the lower surface. To add to the confusion, the upper ellipse has its major axis labelled 'd' which usually denotes the diameter of a circular surface, while the lower ellipse has its semimajor axis labelled 'r' which similarly denotes a radius, even though the ellipses drawn have neither diameter nor radius. The 'h' denoting height is also used for both rectangles and solid objects.

The non-overlapping parts of the 2D shape are composed of the rectangle, half of the top ellipse and half of the bottom ellipse. The area of the rectangle is dh, and the area of an ellipse with semimajor axis d/2 and semiminor axis r. The equation for this area is A = d(πr/2 + h), which is captioned below the figure.

A 3d right circular prism (cylinder) would have a volume of πr2h and a surface area of 2πr2 + πdh, or 2πr(r + h) since in this case d = 2r. The area of each flat surface would be πr2. If we do not assume d = 2r, then the lateral surface area of the right elliptic cylinder is 4h ∫01 √(1 - t²(1-4r²/d²)/1 - t²) dt. The volume is π/2 rdh.

Bottom right.&emsp;A convex hexagon with three pairs of parallel sides and two right angles at opposite vertices (illustrating a rhomboid-based prism). The area of the rectangle representing the front face of the prism is bh. The area of the upper parallelogram is db sin θ. The area of the right parallelogram is dh cos θ. The equation for this area is A = bh + d(b sinθ + h cosθ) as is given below the figure. The surface area of the prism would be 2bh + 2db sin θ + 2dh. The volume is bdh sin θ. Assuming a 3D shape, θ can be artificially altered by the projection; the assumption could be made that θ is 90 degrees, and sin θ is 1 (and therefore can be eliminated from the formulas), but since θ is marked, such an assumption might not be valid.

In the history of the development of computer-generated 3D graphics, calculations of the apparent visual area taken up by the projection of a volume may have been useful in occlusion-like optimizations, where each drawn pixel may be passed through many fragment shaders.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[Four figures in two rows of two, each depicts a two-dimensional representation of a three-dimensional object, with solid lines in front and dotted lines behind. Each figure has some labeled dimensions represented with arrows and a formula underneath indicating its area. Above the four figures is a header:]
:Useful geometry formulas

:[Top left; A circle with a concentric ellipse sharing its horizontal diameter. The major axis of the ellipse is horizontal. The edge of the ellipse above the major axis is drawn with a dotted line, while the lower edge is drawn with a solid line, similar to textbook depictions of a 3D sphere. The shared radius/semi-major axis to the right of the centre is drawn as an arrow and labelled 'r'. ]
:A = πr²

:[Top right; An ellipse with horizontal major axis, plus two straight lines: one from each end of the major axis, up to a point vertical to the centre of the ellipse, so that the major axis of the ellipse (not drawn) and the two lines would form an isosceles triangle with a vertical axis of symmetry. The upper edge of the ellipse above the major axis is drawn with a dotted line, while the lower edge is drawn with a solid line, similar to textbook depictions of a right elliptical cone, or more commonly a right circular cone. The semi-minor axis of the ellipse is drawn with an arrow down from the centre and labelled 'a' and the semi-major axis is similarly drawn to the right of the centre and labelled 'b'. To the right of the shape, the height of the isosceles triangle is drawn using arrows, and labelled 'h'.]
:A = 1/2 πab + bh

:[Bottom left; Two ellipses of the same dimensions, with major axes horizontal, drawn vertically one above the other, with vertical lines connecting each end of the major axis of the top ellipse to the corresponding points on the bottom ellipse. The upper edge of the bottom ellipse above the major axis is drawn with a dotted line, while the lower edge is drawn with a solid line, similar to textbook depictions of a right elliptical prism or, more commonly, a right cylinder (circular prism). Inside the shape, the major axis of the upper ellipse is drawn as a double-ended arrow and labelled 'd'. The semi-minor axis of the lower ellipse is drawn as an arrow down from the centre and labelled 'r'. To the right of the shape, the length of the vertical lines is replicated using arrows, and labelled 'h'. ]
:A = d(πr/2 + h)

:[Bottom right; Two rectangles of the same vertical and horizontal dimensions, drawn with one offset diagonally to the upper right of the other, with diagonal lines connecting the corresponding vertices, forming a hexagon with opposite sides parallel. The upper right rectangle has its left and bottom sides drawn with dotted lines, and a similar dotted line is used connecting the bottom left corner of the two rectangles, similar to textbook depictions of rhomboid-based right prisms, or more commonly rectangular prisms. Outside the shape, the bottom edge of the lower rectangle is redrawn below the shape with arrows and labelled 'b'. The length of the left edge is similarly redrawn to the left and labelled 'h'. The length of the diagonal line connecting the upper left corners of the two rectangles is similary redrawn on the top left using arrows and labelled 'd'. The acute angle between the bottom edge of the lower rectangle, and the dotted diagonal connecting the two lower left corners, is labelled 'θ']
:A = bh + d(b sinθ + h cosθ)

{{comic discussion}}

[[Category:Math]]

1114: Metallurgy

2021-08-27T16:15:21Z

172.70.142.239: /* Explanation */

{{comic
| number = 1114
| date = September 28, 2012
| title = Metallurgy
| image = metallurgy.png
| titletext = This exotic blade was wrought from a different fallen star. The meteorite was a carbonaceous chondrite, so it's basically a lump of gravel glued into the shape of a sword. A SPACE sword!
| imagesize =
}}

==Explanation==
The comic explains how weapons would really behave if they were made out of unusual materials. In fantasy stories, using unusual materials for weapons traditionally makes the weapons more powerful and cooler despite limited explanation for exactly why materials of extraterrestrial origin are so superior to their earthen counterparts. The salesman in the comic is [[Beret Guy]] which appears with a beard for only this comic.

The first panel is a reference to a fairly common fantasy trope: the use of iron meteorites for making weapons and armour (for example the sword "Brisingr" of the Inheritance series, "Anglachel" in the Tolkien Legendarium or the panserbjørns' armour in Pullman's Northern Lights). The quality of such metal can be rather hit-and-miss. On one hand, iron from meteorites was often mixed with "terrestrial" iron in the early stages of human development to create relatively high quality steel for swords. Undeveloped metalworking techniques at the time meant that extraterrestrial metal was often more refined and plentiful than man-made metal ingots. With that in mind, however, [http://www.sciencedirect.com/science/article/pii/0016703767901408 research] has shown that meteorites have an abundance of the chemical element Antimony (Sb) which by itself is a very brittle metal and therefore swords forged from metals harvested from meteorites may not be as strong as lore would have one think.

The second panel is a reference to stories set in Middle-earth where sword such as Orcrist, Glamdring or Sting (the swords of Thorin, Gandalf and Bilbo/Frodo) glow blue when Orcs are near. The dagger in question, though, glows because of the radioactive properties of {{w|Actinium}} (Ac) which is also highly toxic. Definitely not a dagger you would want to carry around for your every day battles.

The word "Eldritch" in the third panel means sinister, ghostly, or magical.

The fourth panel mentions that the weapon gives a +2 to a player's attribute. This is a reference to role-playing games in which it is common to find items that are able to improve one's character by increasing desirable attributes. In this case, however, +2 to cancer risk, a consequence of the dagger's radioactivity, would definitely not be considered a desirable attribute to increase. This would hit harder on Randall due to his partner Megan being diagnosed with breast cancer.

In the title text, the salesman tries to sell [[Cueball]] another meteoric blade, this one made from a {{w|carbonaceous chondrite}}. Carbonaceous chondrites are rocky meteors that generally don't contain a lot of metallic iron. The salesman is either stating that the blade is simply a bunch of nonferrous meteor fragments glued together in the shape of a sword, or stating that the iron he got out of the meteor is so full of impurities that it may as well be gravel. However, because it's made of extraterrestrial material he seems confident he'll still be able to sell it on novelty value alone.

==Transcript==
:[Cueball and Megan are in a weapon store talking to a bearded salesman wearing a hat.]

:[Salesman holds up a sword.]
:Salesman: This sword was forged from a fallen star. Antimony impurities make the blade surpassingly ''brittle'' and ''weak''.

:[Salesman holds up a dagger.]
:Salesman: And this dagger is made of metal from a far-off kingdom. It glows blue.
:Off-panel: When orcs are near?

:Salesman: No, always. Radiation from the Actinium content.
:Megan: ...Does it have Eldritch powers?

:Salesman: It gives the wearer +2 to cancer risk.
:Cueball: I think we should find another shop.

{{comic discussion}}
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Cueball]]
[[Category:Physics]]
[[Category:Cancer]]
[[Category:LOTR]]

Talk:2496: Mine Captcha

2021-08-08T20:56:13Z

172.70.142.239:

Mines at:

+----+
| |
|** |
| * *|
| |
+----+

[[User:Ezist|Ezist]] ([[User talk:Ezist|talk]]) 14:42, 30 July 2021 (UTC)

:+1234
:A2 1
:B??3
:C3? ?
:D 1 1
:concur.

AKA

. . . .
* * . .
. * . *
. . . .

Should be mentioned that it's most probably easier to run a script that solves this puzzle that to explain minesweeper to the majority of people, so this captcha seems pretty useless
[[Special:Contributions/162.158.92.72|162.158.92.72]] 15:56, 30 July 2021 (UTC)
: Writing a script to solve Minesweeper is a great exercise and helps to build a guaranteed-solvable game (which, IMO, is a good thing), but it won't usually start with image recognition. I'm not sure how hard it would be to write an image solver, especially if - unlike in this example - you'd need to dig some cells to finish solving it. [[Special:Contributions/108.162.250.59|108.162.250.59]] 16:20, 30 July 2021 (UTC)

I think that it would be better to explain why there is mine in B3 and D3 (due to the ones) because you then have the full solution. I think that the curent explanation isn't complete enough for someone who don't know minesweeper to understand the solution
Maybe it is only me but I think that it would be less confusing to have column marked with letter and line with number. i don't know if there is any standard for that. I am used to excel way of doing it [[Special:Contributions/162.158.50.27|162.158.50.27]] 16:10, 30 July 2021 (UTC)

I am soooo disappointed that the cursed minesweeper game is not playable. [[Special:Contributions/108.162.221.79|108.162.221.79]] 16:13, 30 July 2021 (UTC)

Is something supposedto happen when I click on a box? I tried this in Chrome, IE, and Firefox, and nothing happens. --[[Special:Contributions/172.70.110.170|172.70.110.170]] 16:18, 30 July 2021 (UTC)

Hello. I have edited the image to include flags or bombs to mark the places. But as a new user I am not allowed to upload images.
If somebody is willing to receive them I could email them. [[User:Rps|Rps]] ([[User talk:Rps|talk]]) 17:10, 30 July 2021 (UTC)

The title is eerily similar to Mein Kampf

The explanation repeats "this is hard because in Minesweeper you're supposed to press the buttons without mines" a lot.[[Special:Contributions/172.70.130.108|172.70.130.108]] 18:23, 30 July 2021 (UTC)
:As a native German speaker I do not think the title sounds similar. The German Mein is a bit more open than the English Mine which is spoken a bit longer. Kampf has one syllable and ends with a triple consonant, captcha has two syllables and ends with a vocal. In Mein Kampf the emphasis is on Kampf, in Mine Captcha it is on Mine. Sebastian --[[Special:Contributions/162.158.89.128|162.158.89.128]] 22:26, 30 July 2021 (UTC)

I think that explanation misses the fact that images in captcha are in randomized order and do not match with actual position on real board and are actually, which can be deducted from fact it's using different colors and font, from multiple separate games. Therefore 'solving' it gives no actual information.
[[User:Kalumniatoris|Kalumniatoris]] ([[User talk:Kalumniatoris|talk]]) 20:39, 30 July 2021 (UTC)

Using the Excel numbering, here’s one verbose way of solving it:
If someone is confused, it may be helpful to draw a diagram and follow along, step by step.

Fact 1: C1 indicates that 1 of its 4 open neighbors is a mine.
Fact 2: A1 indicates that 2 of its 3 open neighbors are mines.
Conclusion 1: Looking at B1 and B2, Fact 1 says at most 1 is a mine and Fact 2 says at least 1 is a mine. Therefore exactly 1 is a mine.
Conclusion 2: Looking at the three open cells around A1, we now know from Conclusion 1 that B1 and B2 account for exactly one mine next to A1, so the other mine adjacent to A1 must be in A2.
Conclusion 3: Looking at C1, from Conclusion 1 we know that B1 and B2 account for the 1 mine next to C1, so there can be no mine in D1 or D2.

Fact 3: A3 indicates that 3 of its 4 originally open neighbors are mines.
Fact 4: B4 indicates that 1 of its 4 open neighbors is a mine.
Conclusion 4: Looking at A4 and B3, Fact 3 indicates that at most 1 is empty (or equivalently, that at least one is a mine) and Fact 4 indicates that at most one is a mine. Since these two contain at least 1 mine and at most 1 mine, they must contain exactly 1 mine.
Conclusion 5: Looking at Fact 4, we know that A4 and B3 account for the 1 mine adjacent to B4, so C3 and C4 must be empty.

Fact 5: D4 indicates that 1 of the 3 originally open neighbors must be a mine.
Conclusion 6: Looking at fact 5, we see that Conclusion 5 ruled out 2 of the 3 neighbors, so D3 must be the mine.

(We’ve now determined the state of all cells in columns C and D, as well as A2. We’ve also identified two pairs (B1+B2 and A4+B3) that each contain exactly one mine.)

Fact 6: C2 indicates that exactly 3 of its 5 originally empty neighbors contain mines.
Conclusion 7: From Conclusion 1 we know that exactly 1 of B1 and B2 is a mine, from Conclusion we know C3 is empty, and from Conclusion 6 D3 is a mine. Having accounted for 4 of the 5 neighbors, and 2 of 3 mines, we know that the remaining cell, B3, must be a mine.
Conclusion 8: Based on Conclusion 5 and Fact 3, we can see that exactly one of A4+B3 is a mine and therefore the other two cells adjacent to A3 must account for its other two mines. Therefore B2 is a mine.
[[User:Solid Kalium|Solid Kalium]] ([[User talk:Solid Kalium|talk]]) 00:30, 31 July 2021 (UTC)

I don't think it's that relevant that the captcha-solver shall click on the mines, opposite to the standard game. (The problem obviously is that if you were supposed to click on non-mines, you might simply click the number fields. Assuming that the number of the mines is given, 12 mines+B4:5,B2:8,D2:5 would be a uniquely solvable example, you'd have to infer D4 is free. But this sort of lacks elegance.) [[Special:Contributions/162.158.111.218|162.158.111.218]] 07:42, 31 July 2021 (UTC)

I guess no one thought to mention that it is possible to have technically unsolvable (by logic) minesweeper puzzle boards, either when there is a very high, or very low, concentration, usually at an edge or a corner. I was kinda disappointed that he didn't do that and make it interactive so that the (usually) 50/50 choice always came out wrong, or you had to trick it by clicking down on one (internally making it the mine) and releasing on the other (revealing the now safe square)... or maybe I'm just a sadist >.> [[Special:Contributions/172.69.63.143|172.69.63.143]] 09:12, 31 July 2021 (UTC)

I do not work for this game, I just play it: If you really dig the difficult logic required to solve this minesweeper puzzle, check out Fill-a-Pix. It's essentially huge puzzles exactly like this. There are many avenues of solving this puzzle. 3@A3 & 1@B4 for example, require that A2&B2 both be mines. 1@C1,3@C2,1@B4,and 1@D4 all collectively require that B3 and D3 are mines. C1 & C2 require that there are 2 mines within the 3 cells: B3,C3,D3. The 1's at B4 and D4 force C3 to be empty, and thus B3 and D3 are the only places those 2 mines could be.

What if what's being signed up for is a messageboard for robots, and it is a reverse CAPTCHA; It only lets robots through (although a much better method of allowing only robots is to ask them to factor something like 702923316547 (the factors are 758141 and 927167)). --[[Special:Contributions/172.70.126.68|172.70.126.68]] 01:38, 2 August 2021 (UTC)

My working method:
* A3's 3 and B4's 1 mean A4 & B3 are mutually exclusively mined, forcing confirmation of A2,B2 as the other two definite mines around A3 and excluding C3&4 as alternate mined neighbours to B4.
* This immediately fulfills A1's 2 and C1's 1; the latter of which, in turn proves D1&2 are unmined.
* D4 can only refer to D3.
* C2 is only fulfilled by confirming A3 (nailing B4's ambiguity in the process).
* Done..?
...I'm surprised it's so simple (excluding errors in putting my thoughts down), even for a 4x4, and expected a tricky logic-chain before some initial assumption was confirmed by an "if..., then if..., then if..., but only if the first assumption was right" chain of some kind (e.g. a soft-commit to one or other of A4/B3, which only resolves, or not, after following the repurcusions half way round the rest of the board and back again - which is how I might need to solve a numeric Kakuro (sp?) puzzle, only I actually send both/''all'' soft possibilities around the relevent parts of the puzzle at the same time if I have to do that. Still, it entertained me to unwrap it my own way. [[Special:Contributions/162.158.159.130|162.158.159.130]] 12:20, 2 August 2021 (UTC)

Yo I recreated the board in WoM: https://minesweeper.online/game/795721480 --[[User:CrazyMadlad314|CrazyMadlad314]] ([[User talk:CrazyMadlad314|talk]]) 19:33, 3 August 2021 (UTC)

AxesOff
ClrGraph
"-----MINESWEEPER-----"
"YOU HAVE TO USE 33"
"MINES TO GET A HIGH"
"SCORE"
138→I
0→2
{10,21}→Dim Mat A
{10,21}→Dim Mat B
{1,1}→Dim Mat S
0→C
"# OF MINES (1~151)"
?→J
J→D
Lbl C
0→C
ClrGraph
D→J
Fill(0,Mat A)
Fill(0,Mat B)
Lbl 0
Text 2,2,"-------MINESWEEPER-------"
Text 8,2,"LOADING AND DELIVERING MINES"
Text 14,2,C
Text 14,14,"/"
Text 14,18,J
2+Int (Ran#×8)→S
2+Int (Ran#×19)→T
If Mat A[S,T]<0
Then Goto 0
IfEnd
C+1→C
If C=J+1
Then Goto 1
Else Mat A[S,T]-99→Mat A[S,T]
Mat A[S-1,T-1]+1→Mat A[S-1,T-1]
Mat A[S-1,T+0]+1→Mat A[S-1,T+0]
Mat A[S-1,T+1]+1→Mat A[S-1,T+1]
Mat A[S+0,T-1]+1→Mat A[S+0,T-1]
Mat A[S+0,T+1]+1→Mat A[S+0,T+1]
Mat A[S+1,T-1]+1→Mat A[S+1,T-1]
Mat A[S+1,T+0]+1→Mat A[S+1,T+0]
Mat A[S+1,T+1]+1→Mat A[S+1,T+1]
Goto 0
IfEnd
Lbl 1
1→Xmin
127→Xmax
1→Ymin
63→Ymax
For 2→A To 10
For 2→B To 20
If Mat A[A,B]=0
Then 5→Mat B[A,B]
Text 7A-11,5B-8,0
I-1→I
Goto 2
IfEnd
Next
Next
Lbl 2
1→A
62→B
2→R
2→T
1→V
8→U
... [CODE OMITTED]
Lbl 9
Text 55,2,"YOU LOSE :("
For 2→N To 20
For 2→M To 9
If ((Mat A[M,N]<0)+(Mat B[M,N]=0))=2
Then Text 7M-11,5N-8,"X"
IfEnd
If ((Mat A[M,N]>-1)+(Mat B[M,N]=1))=2
Then Text 7M-11,5N-8,"."
IfEnd
Next
Next
Lbl B
If Getkey=76
Then Goto C
IfEnd
Goto B
Lbl A
Text 55,2,"YOU WIN :)"
If ((C=34)+(Z<(Mat S[1,1])))=2
Then Text 49,2,"NEW HIGH SCORE!"
Z→Mat S[1,1]
IfEnd
Stop