Explain xkcd: It's 'cause you're dumb.
When abbreviating the date into numerical form, various areas of the world tend to list the year, month, and day in different orders (as well as with different delimiting symbols), which can cause confusion particularly when the day value is 12 or lower allowing it to be easily interpreted as the month and vice versa. As a public service announcement, this comic states that there is in fact one international standard for writing numeric dates, set by the International Organization for Standardization in its ISO 8601 standard.
The comic then proceeds to list several discouraged ways of writing out the date of the comic's publication, as they do not match the standard. It begins with several commonly used ones in countries around the world, but then begins to list increasingly uncommon ways, ranging from strange (Roman numerals) to quirky (binary, Unix time) to essentially impossible (painting the numbers onto a black cat).
The title text provides a perfect example of the kind of ambiguity that can arise when non-standard formats are used. The ISO standard was in fact published on 1988-06-05 and amended on 2004-12-01. This is mentioned in the title text in mm/dd/yy format; however, there is no way to naturally figure this out, particularly with the second date. With the year truncated to two digits and all three numbers at 12 or lower, the date may well be interpreted as 12 January 2004, or 4 January 2012.
Date formats was again the subject in 1340: Unique Date.
The other mentioned formats are:
|| MM/DD/YYYY, used mostly in the United States.
|| MM/DD/YY, same as above but with the year shortened to two digits.
|| DD/MM/YYYY, used variously in South America, Canada (officially uses ISO 8601), Australia, New Zealand and Europe.
|| DD/MM/YY, same as above but with the year shortened to two digits.
|| YYYYMMDD, same as ISO 8601 without delimiting punctuation. Allowed by the standard. Technically not ambiguous but is hard to read as a date at first glance.
|| YYYY.MM.DD, used in Japan. Same as ISO 8601 except with different punctuation.
|| DD.MM.YY, used in Germany, Russia, etc.
|| DD-MM-YY, used in Denmark, Netherlands, Indonesia, India, Bangladesh, etc.
|| D.M.YY. It is common in several areas to abbreviate the month or day to a single digit and drop the leading zero when possible.
| 2013. II. 27.
|| YYYY. MM. DD., with month as Roman numerals, used in Hungary.
|| D⁄M-YY, traditional format in Sweden
|| Year and decimal fraction of year. 0.158904109 is a decimal approximation of 58/365, with February 27 being the 58th day of the year. Allowed in ISO 8601 as it is not ambiguous; presumably easier to read for computers/programs but difficult for humans.
|| The ISO 8601 standard but written in Roman numerals. Never used as a traditional standard anywhere as it is hard to read, parse, and interpret for no benefit.
| MMXIII LVII⁄CCCLXV
|| Year followed by its partial fraction 57/365, all in Roman numerals. Equally useless as the above. As a note, apparently this 'standard' is different from the decimal fraction two rows above, as the decimal fraction notation uses the end of the day (first day of the year is 1/365 while the last is 365/365), while this uses the beginning (first day is 0/365 and last is 364/365).
|| UNIX Timestamp, a standard method of storing absolute time in many computer systems and defined as the number of seconds since 00:00:00 on 1 January 1970 (UTC). The Unix time listed here appears to mistakenly be for 2012-02-27, which is also mentioned by Randall in the original transcript.
|| A useless format where the numbers 2013, 2, and 27 written as needlessly long arithmetic expressions using just the digits 1 and 3. For additional confusion, the values are delimited by slashes, enabling confusion with the fraction bar. (If evaluated literally, the entire expression evaluates to 670.963, or 671 minus 1 divided by 27.)
| 2 272013
|| A nearly impossible to read date "format" that can be considered a parody "compromise" between different formats: rather than argue about the order in which the year, month, and day should be, they are simply all written on top of each other. As a "bonus", there is also no arguing over which separator character to use.
|| The US mm/dd/yy format in binary, corresponding to 2/27/13. Never used for obvious reasons.
|| MM/DD/CC/YY, where CC stands for century. This format is never used. Note that while months and days count starting from 1, centuries and years in this format count from 0 for extra confusion. But the CC value is widely used on many operating systems to distinguish between the 20th and 21st century, represented by the values "19" and "20" because 1950 belongs to the 20th century.
|| An obfuscated format where the small numbers indicate the positions where the large digits should be placed. In this reading, 0 is used at positions 2 and 5, 1 is used on position 3, etc.; the result being 20130227
| [A hissing black cat with "2-27-13" painted on it]
|| In Western cultures, black cats and the number 13 are associated with bad luck. The cat might also just be angry that someone covered it in paint.
- Public Service Announcement:
- Our different ways of writing dates as numbers can lead to online confusion. That's why in 1988 ISO set a global standard numeric date format. This is the correct way to write numeric dates:
- The following formats are therefore discouraged:
- 2013. II. 27.
- MMXIII LVII⁄CCCLXV
- 1330300800 [This is the UNIX time for *2012*-02-27, Randall.]
- 2 272013 [the numbers 2013, 02, and 27 written overlapping each other]
- [A black cat with 2-27-13 scrawled across its body in dripping white paint.]
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Apparently there are some mistakes in the Roman numerals in the comic, the year MMXII is 2012. Also LVII/CCLXV = 57/265, whereas February 27th is the 58th day of the year (which has 365 days). --ulm (talk) 07:55, 27 February 2013 (UTC)
- Just guessing, but could this have something to do with the divergence of various Roman calendars, e.g. Julian vs. Gregorian? 18.104.22.168 13:55, 27 February 2013 (UTC)
- Another error: Obviously 1330300800 is intended to be Unix time, but it corresponds to 2012-02-27 00:00:00 UTC. --ulm (talk) 08:10, 27 February 2013 (UTC)
- The day part "57" is not wrong: Since Feb 27 is the 58th day of the year, at the beginning of that day, 57 days have gone by since the year started. (At the end of the day, 58 days have gone by) Since we associate days with their beginning (like we do with e.g. hours and minutes), 57 is the correct number (or else Dec 31 would be 2013+365/365 = 2014, and therefore in the wrong year) -- Xorg (talk) 13:53, 27 February 2013 (UTC)
- The day part is ambiguous. It could be as Xorg suggests, the fraction of the year past at the start of the day. On the other hand it could be interpreted as "day 57 or 365," as with pieces in a shipment or page numbers. In the latter case it should be 58/265. But then, that (ambiguity) is the point, isn't it? Jqavins (talk) 17:40, 27 February 2013 (UTC)
- Meanwhile the comic was replaced, with CCLXV corrected to CCCLXV. --ulm (talk) Prima vigilia, XVI Kal. Mar. MMDCCLXVI
- I was just about to publish my theory of how "2012" in the Roman numerals in just the same vein might be intended to indeed represent the year we denote "2013", but by counting only the finished years. This would also connect with the confusion over year zero, another thing that ISO 8601 tried to straighten out. (They placed it before year 1.) Everything fit so well. Then there was an edit conflict, following Randalls correction to "2013". I guess you can't always be right. –St.nerol (talk) 23:03, 27 February 2013 (UTC)
Can anyone explain 01237 (last interpretation before the cat)? Thanks 22.214.171.124 08:04, 27 February 2013 (UTC)
- The small numbers above and below the larger ones show which digit is used where. For example, the 2nd and 5th digit is a 0, the 3rd digit is a 1 etc. 126.96.36.199 08:15, 27 February 2013 (UTC)
- 01237 are the digits used in the date, and the numbers above and below them reflect the order in which they are written; 0 is the second and fifth digit, 1 is the third digit, 2 is the first, sixth and seventh digit, 3 is the fourth digit, and 7 is the eighth digit: 20130227 Bdemirci (talk) 08:15, 27 February 2013 (UTC)
Someone can explain me what means: ((3+3)×(111+1)-1)×3/3-1/33? -- 188.8.131.52 (talk) (please sign your comments with ~~~~)
- Read the comic explanation. Davidy²²[talk] 10:58, 27 February 2013 (UTC)
Many of these format mirror how the dates are spoken in languages. For example, Americans will say "February 27, 2013" and write "2/27/2013", whereas the French will say "27 février 2013" and write "27-02-2013". As a scientist, I was encouraged to write "27 II 2013" (which is apparently standard in Hungary, according to the explanation above) in my lab notebook to avoid ambiguity. --Prooffreader (talk) 13:16, 28 February 2013 (UTC)
A strange thing is that he forgot the form mostly used in Europe: 27.01.2013. --DaB. (talk) 12:44, 27 February 2013 (UTC)
- That form is mostly used in Germany. Belgium and France use 27/01/2013 more, Netherlands use 27-01-2013. No idea what the UK prefers although I could imagine 01.27.2013.62.159.14.62 12:58, 27 February 2013 (UTC)
- The UK prefers 27/02/2013 --H (talk) 13:20, 27 February 2013 (UTC)
- That form (27.02.2013) is also common in all of Scandinavia. --Buggz (talk) 14:15, 27 February 2013 (UTC)
The image text has a subtle twist as "12/01/04" offers no contextual clues to it meaning at all, can be read three different ways : "December 1st 2004", "January 12, 2004" or "January 4th, 2012" (as opposed to, for example, "01/15/98" which could only be interrupted as "January 15th, 1998") JamesCurran (talk) 14:29, 27 February 2013 (UTC)
- Technically speaking, it could also be interpreted as April 1st 2012 or April 12th 2001, though that would be the least likely interpretation. I personally like spelling out 3 letters of the month and using an apostrophe before the year, such as 27 Feb '13. --Joehammer79 (talk) 15:07, 27 February 2013 (UTC)
- And of course December, 4th 2001 Sebastian --184.108.40.206 19:54, 27 February 2013 (UTC)
Is there any way to convert the time-stamp placed on these comments to the YYYY-MM-DD format? --16:17, 27 February 2013 (UTC)
- If you're logged in, you can set your date and time preferences. I doubt it will affect the timestamps on this page, though, since those appear to be saved as plain text. --Aaron of Mpls (talk) 23:01, 27 February 2013 (UTC)
I feel like the cat thing is a reference to something, but I'm not sure what... is it something? A quick google image search pulls up nothing. --Jeff (talk) 17:26, 27 February 2013 (UTC)
- Seems to me that Randall missed an opportunity: Why a cat? Why not a bobcat? It still could be some other reference that I'm missing too.
- Black cats are considered unlucky. I don't see any reference beyond that. Mattflaschen (talk) 17:59, 27 February 2013 (UTC)
- It's taking the last two digits from 2013 and emphasizing triskaidekaphobia. Doing a web image search on "Cat 13" will pull up similar artwork of hissing black cats combined with the number 13, including both flyers for Friday 13th drink specials at bars, and combat airplane noseart. Apparently combining the unlucky "13" with an unlucky black cat emphasized that they were bad luck for the enemy. Columbus Admission (talk) 19:20, 27 February 2013 (UTC)
- "You're a Kitty!" http://www.explainxkcd.com/wiki/index.php?title=231
- The cat's "Hissss" could be a reference to timestamp formats in PHP web programming, where the desired date format is generally followed by "H:i:s", the standard 24-hour time format. That would explain the specifically lowercase "i" in the cat's hiss.220.127.116.11 13:28, 22 March 2013 (UTC)
Cool, this is my birthday. Mattflaschen (talk) 17:59, 27 February 2013 (UTC)
"However the list then starts listing formats ranging from uncommon to absurd, such as writing the date partly in Roman numerals [...] " -
My math teacher uses a very similar format (in reverse order, d/m/yy, with m being in Roman numerals, because this is Germany (see above)), so I wouldn't call it absurd. She is the only person I know who uses it though. 18.104.22.168 19:36, 27 February 2013 (UTC)
The image and explanation needs to be updated for the corrections. I could do the explanation part, but I have no idea how to do the image part. And one without the other would be confusing for the readers, so I'll leave that to wiki-magic. 22.214.171.124 21:09, 27 February 2013 (UTC)
- I updated the image as well as the explanation (and transcript). There is still the error on the Unix timestamp though (will this comic be fixed a third time?...). - Cos (talk) 21:57, 27 February 2013 (UTC)
Sweden uses the ISO 8601 format. (If only food producers could understand this as well..)
126.96.36.199 21:42, 27 February 2013 (UTC)
- What can we learn from this? - I've learned that no matter the system we use today to communicate with others, it's probably seems silly for someone else. It's great to document what we do and propose it as an option to others, but it will be next to impossible to force them to adopt. When someone will develop a time reference that makes sense to everyone, it will be adopted all over the world without much effort. - e-inspired 188.8.131.52 19:07, 27 February 2013 (UTC)
Perhaps the cat (because of the vagueness of the system) was referring to not the 27th of February 2013. but instead referring to the 13th of February in 1327 which would make it Friday the 13th. -- 184.108.40.206 (talk) (please sign your comments with ~~~~)
Just so you know, Explainxkcd wiki uses the ISO certified date standard for its "All Comics" page. Davidy²²[talk] 01:57, 28 February 2013 (UTC)
Personally I've always preferred to use Year-Month-Day my personal stuff. I like it because the format is written the way we write any other number: Most significant to left, least significant to right. I didn't know this was a standardized method and I've always wondered why it wasn't used. Nice to know it is!220.127.116.11 04:09, 28 February 2013 (UTC)ExternalMonologue
Personally, I like yyyy-mm-dd because it sorts correctly. I really hate running into a list of dates sorted by month name, or worse, day of the week. I suspect this was part of why ISO chose this format. I've never been able to remember the american vs european ordering... My only other options is: February 27, 2013. Divad27182 (talk) 12:11, 28 February 2013 (UTC)
- I'm not sure what standard the Canadian Military officially uses, but as soldiers we were all taught to use a "7 Feb 2013" format when writing dates. Seems the most clear and concise to me. -- 18.104.22.168 (talk) (please sign your comments with ~~~~)
- Most of the dates I've seen used by the Canadian Military have been of that format but have only used 2-digit years - e.g. 27 Feb 13 (they didn't learn from Y2K!) -- 22.214.171.124 (talk) (please sign your comments with ~~~~)
- What can we learn from this? - I've learned that keeping our time relative to earth rotation is outdated, we keep having to add seconds here and there just to keep time. And as an engineer don't get me started on complexity of mktime function. I personally think of time as oscillation of a flawed crystal in my circuits that I constantly need to keep accounting for through endless calibrations, and keep wishing that better time references would be cheaper (to me good is never good enough) - E-inspired (talk) 15:05, 28 February 2013 (UTC)
Ha ha E-inspired you should read the "falsehoods programmers believe about times" http://infiniteundo.com/post/25326999628/falsehoods-programmers-believe-about-time http://infiniteundo.com/post/25509354022/more-falsehoods-programmers-believe-about-time-wisdom 126.96.36.199 20:14, 28 February 2013 (UTC)
- Dude, you've just made my DAY! I forgot the last time I've laughed as hard. Why didn't I know about this site before? - E-inspired (talk) 20:43, 28 February 2013 (UTC)
Why is the date of this comic written as "February 27, 2013" and not "2013-02-27"? 188.8.131.52 08:46, 14 March 2013 (UTC)
The hover hint says "ISO 8601 was published on 06/05/88 and most recently amended on 12/01/04." which must be a joke - because it is impossible to know whether these days are 6 May 1988 and 12 January 2004 or 5 June 1988 and 1 December 2004. Why make a comic about ISO 8601 then use ambiguous dates in the hint? 184.108.40.206 (talk) (please sign your comments with ~~~~)
Amateurs, you don't put periods in format with roman month number. So it's 27 II 2012 220.127.116.11
12:48, 20 April 2015 (UTC)