Editing 2888: US Survey Foot

{{comic
| number    = 2888
| date      = January 31, 2024
| title     = US Survey Foot
| image     = us_survey_foot_2x.png
| imagesize = 740x606px
| noexpand  = true
| titletext = Subway refuses to answer my questions about whether it's an International Footlong or a US Survey Footlong. A milligram of sandwich is at stake!
}}

==Explanation==

This comic pokes fun at the difference in length between the {{w|Foot_(unit)#U.S._survey_foot|US Survey Foot}} and the {{w|Foot_(unit)|International Foot}}. After Carl Edvard Johansson's {{w|Carl_Edvard_Johansson#Johansson_and_the_inch|gauge blocks}} in 1912 led to {{w|International_yard_and_pound|an international agreement}} in 1959, the foot has been defined to be exactly 0.3048 meters, whilst the US survey foot continued to use the {{w|Mendenhall Order|definition of 1893}}, making it a bit longer than the international foot at 1200/3937 meters. However, the difference between the two is proportionately too small to be meaningful for most purposes, as they differ by only 2 parts per million. At foot-length scales, the difference is a fraction of a micron, with longer measures (where the error grows to a notable degree) requiring an already excessive implied precision likely to mismatch its true accuracy. Some engineering or scientific applications ''may'' involve such tolerances, but would be expected to consistently use some more modern standard of measurement, such as {{w|International System of Units|SI (the Metric System)}}, to {{w|Mars Climate Orbiter|avoid such confusion}}.

In the third panel, Cueball says that someone is using the survey foot again. It turns out to be [[Black Hat]], acting in a way that sounds very typical for him. Cueball claims that he is drawing the world 610&nbsp;nm closer to madness, which is about the difference per foot between the two measures. Cueball, outraged, then says that the {{w|National Institute of Standards and Technology}} (NIST) will capture Black Hat to stop him from using the US survey foot. One joke here is that his coordinates show that he is 8000 miles away, but since he is using the US survey foot, he is 0.016 miles (around 25.75 meters or 84.48 feet) away from the search team, making them unable to find him at that exact spot. They are probably at the same lake in the last two frames, with maybe only some bushes separating them; a good strike team would likely keep looking in the area, but perhaps being strictly NIST-trained to adhere to particularly exacting standards has ironically made them vulnerable to the same inaccuracies that they are supposed to be preventing.

Part of the joke is the imaginative idea that NIST employs and dispatches strike teams to apprehend persons that use incorrect measurements. This may be a play on words about the {{w|Nuclear Emergency Support Team}}, or "NEST", a {{w|United States Department of Energy}} group who respond to nuclear and radiological emergencies such as reactor accidents or nuclear terrorism, and who might reasonably have access to resources such as the helicopters depicted during a crisis.

The title text references a {{w|Subway (restaurant)#Sandwich_size|2013 lawsuit}} over the length of a "Footlong" sandwich sold by the Subway fast food chain. However – in contrast to the issue at stake in that lawsuit – the difference in length between an 'international footlong' sandwich and a 'US survey footlong' sandwich is far below the precision ''or'' accuracy by which sandwiches are usually produced, making it understandable that Subway would not think it necessary to clarify which definition of 'foot' they use for their products.

Absurd outcomes from updated survey standards was also the topic of [[2920: Survey Marker]].

===Explanation of the comic's underlying assumptions and implications===
Randall appears to be playing a bit fast-and-loose here. To make this joke work implies a rather imaginative situation: that both Black Hat and the searchers have set their devices to measure and report location in reference to the same location (the place where Cueball is, at one end of the 8,000 mile measurement) and not just use a satellite navigation system like GPS and lat/long like every other smartphone on the planet. 

In the unlikely event that the searchers' phones measure and report location in reference to Cueball's location, evidently Black Hat has also overridden his device's in-built GPS to report its location in reference to Cueball's location as a way to toy with him and the NIST teams, and then traveled EXACTLY 8,000 survey-foot miles away, knowing NIST would be able to track him and that a team would be sent in pursuit. After all, Black Hat is known for his preternatural powers of mischief.

Though Cueball’s location is not specified, one potential location is NIST headquarters in Gaithersburg, Maryland, or another governmental location, perhaps in the Greater Washington Area where most US government agencies and departments are headquartered. These options are supported by the panel in which Cueball mentions a NIST team is on their way and brags that “we” are going to capture him. This language implies that Cueball either works for NIST or for a larger effort in which NIST is a partner. These location options are also supported by the fact that Cueball’s location is used for the origin point of the 8,000-mile measurement, suggesting that he’s speaking at a flagship location and not a random office building.

The use of helicopters — which cannot fly 8,000 miles unaided — also suggests an imaginative situation in which NIST teams with access to helicopters are distributed around the globe, perhaps at US air bases and on US aircraft carriers.

===Real world examples===
In the early 2000s, Survey Foot/International Foot conversion issues created difficulties in the civil engineering industry after a commonly used CADD design software package changed how it processed units. Prior versions of the software program Microstation were unit-agnostic, relying only on absolute coordinates assigned to elements from survey data. Starting with Microstation Version 8, internal software calculations were performed entirely in metric units and relied on a units definition file to seamlessly convert to the unit system being used for a project. The default options in the program being “Foot” (i.e., International Foot) or “Survey Foot”, many users were unaware of the difference and selected “Foot” even when a project’s field survey was performed in survey feet. In the US, most states have their own coordinate systems, referred to as State Plane Coordinates, to correct for the approximation of projecting the Earth’s spherical surface into a cartesian X,Y plane. Some states have coordinate zones which span their entire length, so a project’s coordinates can be millions of feet from the origin, a scale on which the minuscule difference between Survey and International feet conversion becomes whole feet.

In another famous example, a building in Arizona was required to be built one story shorter than planned.  The building was going to be 20 stories tall and almost in line with an international airport runway.  It was designed to be one foot north of the FAA mandated flight path for runway approaches, which it would otherwise violate due to its height.  However, the building was surveyed in international feet (the legal standard in Arizona) while the flight path was defined in survey feet (used nationally by the FAA).  The baseline that defined coordinates in this part of Arizona was about a million feet away, which added up to a difference of about two feet.  As a result the building would have been inside the FAA flight path, and to avoid this the building had to be reduced to 19 stories so it was below the exclusion zone.

==Transcript==

:[Closeup on Cueball.]
:Cueball: We thought it was over. After 60 years of struggle, the US survey foot was dead, deprecated by NIST in 2023.

:[Cueball is shown to be talking to Ponytail, Hairy, and Megan. He has a presentation behind him.]
:Cueball: We thought architects and engineers could rest easy, free of the headaches of having two conflicting definitions of the foot that differ by 610 nanometers.
:International foot: 0.304 800 000 m
:US survey foot [crossed over in gray] <span style="color:gray">R.I.P.</span>: 0.304 800 609... m

:[Cueball points at an image of Black Hat with unreadable writing above it.]
:Cueball: But I bring dire news:
:Cueball: ''Someone has started using the US survey foot again.''

:[Closeup on Cueball again.]
:Off-panel voice: Why!?
:Cueball: We don't know.
:Cueball: Some people just want to drag the world 610nm closer to madness.

:[Farther view of Cueball only. He clenches a fist.]
:Off-panel voice: What can we do!?
:Cueball: A NIST team is already in the air. We will capture the scofflaw and end this nightmare.

:[Two helicopters flying, with mountains in the background.]

:Caption: 8,000 miles away
:[Two operatives in a forest by a pond with NIST helmets. One talks on a walkie-talkie.]
:Operative: We've reached the coordinates of the target's device. There's no one here.
:Voice from walkie-talkie: How!?

:Caption: 8,000.016 miles away
:[Black Hat walking elsewhere in the forest, apparently by the same pond. He appears to be holding a device of some sort.]
:Black Hat: ♫ ♪

==Trivia==

The number of miles in the last panel was [https://www.explainxkcd.com/wiki/images/archive/5/5f/20240131173446%21us_survey_foot_2x.png originally] 8,000.014, but was changed to 8,000.016. The latter matches the 2 ppm difference between the international foot and the US survey foot.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Hairy]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Black Hat]]
[[Category:Characters with hats]]
[[Category:Geography]]
[[Category:Food]]