
Ending the Era of the U.S. Survey Foot - amjaeger
https://www.nist.gov/pml/us-surveyfoot
======
p1mrx
> In 1959, the relationship of the foot to the meter was officially refined as
> 1 foot = 0.304 8 meter exactly.

We can thank one man for this: Carl Edvard Johansson from Sweden. When making
gauge blocks, he decided to round off the inch to exactly 25.4mm, and people
around the world used his blocks to manufacture everything. The 1959 change
just reflected what industry was already doing.

\- [http://mitutoyo.com/wp-
content/uploads/2013/07/E12016-Histor...](http://mitutoyo.com/wp-
content/uploads/2013/07/E12016-History-of-The-Gage-Block.pdf#page=8)

\-
[https://books.google.com/books?id=3rUaAQAAMAAJ&lpg=PA293&ots...](https://books.google.com/books?id=3rUaAQAAMAAJ&lpg=PA293&ots=hiqJuRiYSM&pg=PA293)

~~~
samatman
It frustrates my sense of aesthetics to no end that the inch isn't defined as
25.6 mm.

That would make the imperial system a base-two variant of the SI system.

This would have made the mile around 42 (current) feet longer, which is a non-
starter; I just wish the foot had been a little longer, somehow.

~~~
sdenton4
If it helps, the miles-to-kilometers ratio is approximately the golden
ratio... (1.609 vs 1.618.)

So, as a level N nerd, you can convert miles to kilometers by rounding to a
nearby fibonacci number, and then finding the NEXT fibonacci number (and maybe
fudging a bit in the direction of rounding).

Then, as a Level N+1 Nerd, you can realize that the Fibonacci Base exists, in
which any integer can be represented as a collection of distinct fibonacci
numbers. (for example, 43 = 34 + 8 + 1, or, using a binary string to show
which Fibs are involved, 42 = 10010001.) The conversion of miles to kilometers
is then just a bit-shift operation.

Well, almost, anyway.

~~~
samatman
It doesn't help! If the inch were 25.6mm, the ratio would be 1.622!

That's a lot closer! argh!

------
opwieurposiu
As an example of a problem that can occur: Client wants to survey the
elevations of a parcel of land for building a house. The surveyor goes out and
collects data with gps survey equipment, which produces a .csv file of
northing,easting,and elevation values relative to some National Geodetic
Survey benchmark. The engineer imports this .csv into his cad software,
produces a grading plan .csv file. The earthmoving contractor imports the
grading plan into his software and grades the site.

Client gets house built, moves in and discovers that the front yard turns into
a swamp after every rain.

Somewhere in the chain of importing and exporting .csv files, software A was
using survey feet and software B was using international feet.

This can also cause problems like structures built in the wrong spot, fences
built on neighbors land, etc.

~~~
abofh
The difference is .0002%. your examples would barely add up to an inch over a
mile.

~~~
opwieurposiu
Sometimes the benchmark for northing/easting/elev is many miles away from the
actual site. This is especially true with gps surveys.

It only takes a few inches to wind up with a substantial drainage problem.

~~~
function_seven
Wouldn't the elevation difference between benchmark and site be the important
bit here? If so, then the difference would rarely be more than a mile, and the
resulting error would be at most an 1/8"

~~~
opwieurposiu
It has been 20 years since I worked in this area so likely I have some details
wrong. If elevation is distance to the center of the earth 1/8" per mile is 40
feet!

From the link below you can see the noaa benchmark is using both elevation in
feet above sea level and in meters from the center of the earth.

[https://www.ngs.noaa.gov/cgi-
bin/ds_mark.prl?PidBox=aa3449](https://www.ngs.noaa.gov/cgi-
bin/ds_mark.prl?PidBox=aa3449)

~~~
beerandt
If you're not converting H (gps orthometric height) to E (local elevation
datum to "sea level") first, you're doing it wrong, for a number of practical
reasons.

Usually there's not even a reason to use H directly anymore, since elevations
should reference a local benchmark.

GPS has changed things, but surveyors are still obscenely practical when it
comes to procedures for eliminating systematic error.

~~~
1-6
Using an RTK-GNSS requires a gravitational model of the earth to measure mean
sea level (MSL). Using your position, you use the GEOID model to figure out
the delta of the nav satellite's orbit to the MSL.

~~~
beerandt
Yes, That's what I mean by going straight from H to e first. The geoid is that
conversion.

Although for rtk, the delta isn't to any of the sats, it's to your base
station. The deltas to the sats cancel out of the equations, which is where
most of the gains in accuracy come from. But it still needs to be tied into a
known elevation benchmark.

That said, most field crews will still be shooting a differential to a
published benchmark, or plugging the geoid file into the data collector, or
dialing into a vrs or cors that already is adjusting for the geoid. For them,
H is just an extra data point asking to be plugged into the wrong data field.

Unless you're doing static observations or geodesy or manual network
adjustments or direct gravity readings, the new way (22) isn't all that
different from the old way (83). There's just different underlying theory of
MSL and different math to adjust the network. And if you _are_ doing any of
those things, then you generally already know what you're doing.

------
yathern
If anyone else is curious - the "US Survey Foot" was 609nm larger than the US
International Foot. Or, 0.0002% Larger.

~~~
whatshisface
It would take 41,708 feet for the error to add up to one inch.

~~~
twic
Which feet?

~~~
killjoywashere
The left ones.

Sorry, I'll show myself out.

------
seancoleman
I actually learned of the difference between the U.S. Survey Foot and the
International Foot while working on
[https://plantpredict.com](https://plantpredict.com). For years we had
infrequent but bizarre unit-conversion bugs. Calculations literally weren't
adding up. We assumed it was related to precision rounding since numeric input
fields showed rounded values. It turns out the imperial-to-metric feet
conversion factor we picked was 1 of 2 choices, and we picked wrong!

------
DoofusOfDeath
The article left me confused about what it means to have a legally binding
redefinition of a term.

Does this mean that all existing, legally binding contracts are to be
reinterpreted using the new definition of "foot"?

Does it mean that any _new_ legal document (contract, legislation, etc.) that
uses the term "foot" without further clarification shall be assumed to mean
this new definition of "foot"?

~~~
oh_sigh
As a general point, I don't think contracts can have their terms adjusted
after the fact without both parties agreeing to it.

~~~
ska
This seems the only reasonable way to do it except for terms deemed
unenforceable (which is why you see a lot of boilerplate about severability)

------
alleycat5000
A good overview on NSRS can be found below, pretty interesting read if you're
into datums.

[https://www.esri.com/about/newsroom/arcuser/moving-from-
stat...](https://www.esri.com/about/newsroom/arcuser/moving-from-static-
spatial-reference-systems-in-2022/)

------
Animats
Fortunately, the inch is defined as 0.0254 meter exactly. So we have
consistency for the really important units.

~~~
AnimalMuppet
Then which "foot" is exactly 12.000000 inches?

~~~
mark-r
My calculation shows 12 * 0.0254 = 0.30479999999999996 meters. That may be off
a little due to IEEE floating-point inaccuracy.

~~~
d-sc
2 * 4 = 8 so the last significant digit should be an ‘8’

~~~
pjc50
Definitely one to cite in the "overreliance on calculators" \- the comment you
are replying to should have realised that multiplication can't create digits
to the right like that!

(Most desktop calculators do it in BCD which would give the correct result,
too)

~~~
mark-r
I use Python as my desktop calculator. It has a Decimal module that would have
gotten it correct, but that would have been way too much trouble.

------
jessaustin
Thank you 'amjaeger for removing the local-TV-news-level attempted pun from
the headline.

------
ska
Ah, the joy of standards.

------
alamortsubite
If someone had told me this statement was part of a Monty Python script, I'd
likely have believed them.

~~~
Infernal
For those of us who came later to the discussion, what was the original title?

~~~
alamortsubite
I was referring to the content of the post on nist.gov. But I think the title
has changed, and may have been simply "U.S. Survey Foot" when I first
commented.

------
hadlock
Mildly surprising that we are not just using meters at this point.

~~~
zamalek
The situation is far more bizarre than "use" or "not use." As I understand it,
America uses something along the lines of "converted metric units" \- i.e. the
entire imperial system is defined according to metric/SI. Some subset of
public records have been, supposedly, converted to metric. If you have a
recent car, it should have km/h alongside mph (in a smaller font, or as a
different digital readout). You'll find metric all over the place if you keep
an eye out for it.

~~~
moron4hire
It's called "US Customary", not "imperial".

~~~
Taniwha
Only in the US - except for gallons/fluid ounces - those genuinely are US only

~~~
moron4hire
No, that's my point. The system of units that is used in the United States is
not "Imperial", it has differences from Imperial. We use "US Customary".

------
DeepYogurt
Imagine it being 2020 and not using the metric system.

~~~
adamtj
That's not hard to imagine. Quick, what's 1/3 of a meter? The sometimes
problem with metric is it's base-10. The prime factors of 10 are 2 and 5. Feet
are in base-12, which has the prime factors 2 and 3. Three is much more useful
than five. There are marks on your measuring tape at exactly 1/3 of a yard or
1/3 of a foot.

Metric is often easier and more convenient, but not always. So, in the US, we
tend to use metric or customary units depending on which is more convenient
for the task at hand. Actually, it's a lot like the UK and other countries
where older systems still exist alongside metric. The difference with the US
is that we don't have as many unnecessary laws mandating metric. You're an
adult. You're working with other adults. You're perfectly capable of figuring
out what to do without the input of lifelong politicians who've never measured
a thing in their lives. Except for the amount of your money that they're going
to spend. They like measuring that.

~~~
mrb
My wife's family, who almost all have university degrees, who were all born
and raised in the US, and who are very familiar with the imperial system NEVER
seem to be able to do math with it. They ask me, a European raised with the
metric system, for help.

Find out how many fl oz of milk are in a measuring cup graduated in units of
cups? Ask mrb.

Convert my daughter's height from feet/inches to inches? Ask mrb.

Convert a package's weight from oz to lb/oz? Ask mrb.

Need to know how cold it needs to be outside in farenheit for water to freeze?
Ask mrb.

I lost count of the number of times they accidentally mix up for example 1.3
feet with 1 ft 3 in. Sometimes it's due to miscommunication, eg. I have seen
"six pound five" interpreted as 6 lb 5 oz by one when the speaker meant 6.5
lb. Or vice versa.

It's just comical to see someone trying to argue that the imperial system is
"sometimes easier."

~~~
nwallin
> Find out how many fl oz of milk are in a measuring cup graduated in units of
> cups? Ask mrb.

8\. Volume is base 2. Two tablespoons in an ounce, 8 ounces in a cup, (there
used to be other units in between, but nobody used them, like deci in si) two
cups in a pint, two pints in a quart, four quarts in a gallon.

If you were going to sell me on switching units, it would be based on
hexadecimal instead of base 10.

> Convert my daughter's height from feet/inches to inches? Ask mrb.

5' is 60". Add and subtract from that. 5'6” is 60"+6" = 66" inches, 4'4" is
60"-8"=52", etc. "Normal" humans cluster around 5' so this takes you pretty
far.

> Convert a package's weight from oz to lb/oz? Ask mrb.

Again, base 2. As a programmer this is easy because it leverages all the same
neural pathways that I use for converting between base 10 and base 2/16\.
Hell, maybe learning to cook in base 2 has made me a better programmer.

> Need to know how cold it needs to be outside in farenheit for water to
> freeze? Ask mrb.

This is definitely the worst example. 0°F is really cold. 100°F is really hot.
Fahrenheit is objectively better than Celsius as a common parlance unit.

> I lost count of the number of times they accidentally mix up for example 1.3
> feet with 1 ft 3 in.

I've never seen anyone do this ever. I've seen dumb computer systems do shoddy
conversions on inputting numbers into a program, but that's why you normalize
your inputs and show it back to the user. I've never seen or heard of a living
breathing human make this mistake.

> "six pound five"

That's like saying "100 centi 57 meters". Those words have meanings on their
own, but they don't have a meaning in that order. The only meaningful response
to that is to be confused, and then realize they're confused.

How long did they live in the US and how long have they lived where they are
now? This sounds like someone who lived in the US until they were ten and
moved somewhere where they not only didn't use customary units but didn't
speak English. Then spent the next few years scrambling to master the language
and hit adulthood understanding neither US customary units nor metric units.

Honestly, culture, customs, and normality run deep. Those handful of nations
that use , as the decimal separator and . as the thousands (or otherwise)
separator would have a much easier time and much more benefit swapping their
separators than the average American would switching from customary units to
SI. Nearly everybody uses a 24 hour day, 60 minute hour, 60 second minute.
3600 second hour, 86400 second day, etc.

Oh did I say 24 hour day? Well I lied but it's close enough.

Astronomers happily use astronomical unit, light-year, parsec, and z= redshift
to measure distance all in the same context. For me, having "dumb, arbitrary"
units is way less important than having familiar units. Despite the fact that
humans are dumb and arbitrary, we're still pretty clever.

Most of the people who complain strongly about customary units, which are dumb
and arbitrary, speak languages where inanimate objects have gender. (for the
record, I also think grammatical gender is dumb and arbitrary in English)
"Auto" (meaning car) is neuter and "Wagen" (meaning car) is masculine. If one
considers a scale where 100°F is really hot and 0°F is really cold a dumb,
arbitrary system, you should stop to consider whether to_lower(str) and
to_lower(to_upper(str)) yield the same results.

Humans are dumb, arbitrary creatures. The fact that US customary units are
tend towards base 2 units instead of base 10 is way less arbitrary than
daylight savings time, or the fact that France is in the wrong time zone, or
the fact that Denmark has enshrined in law its own national time basis and
then completely ignores it and then refuses to change the law which is ignored
by literally every single person in Denmark.

~~~
mrb
The conversion techniques you explained, I use them myself (that's why they
always ask for my help, I can do it in my head.) But the fact many Americans
are unable to do that is, in itself, evidence the imperial system doesn't work
that well for them.

> This is definitely the worst example. 0°F is really cold. 100°F is really
> hot.

This might be a sufficient explanation to give to a 5-year-old, but as soon as
you need to do actual work with temperatures, this doesn't work so well. Case
in point: many Americans don't know the freezing and boiling point in ⁰F. So,
no, it's not "objectively better."

> That's like saying "100 centi 57 meters"

No European ever says this. In contrast, many American routinely say "six
pound five".

> How long did they live in the US and how long have they lived where they are
> now?

Their whole life. Born and raised in America.

~~~
Gormo
American here. I've never once in my 40 years on this earth heard someone say
"six pound five". That parlance is often used for _feet and inches_ (almost
always in reference to human height), but I've never encountered anyone using
it for pounds and ounces.

~~~
nkurz
I'm American, have lived in many parts of the US, and I agree: "six pound
five" is not something that we say. As Gormo says, this construction is
frequent for feet and inches ("six foot five"), but would not be standard for
weight.

And personally, if I were to use this nonstandard construction, I'd probably
pluralize "pounds". I don't know why "foot" is usually singular in the
parallel construction.

The most charitable interpretation I can come up with is that your relatives
are from the American South, and are actually saying "six point five", meaning
6 and half pounds, and you are mishearing them.

------
jackfoxy
I knew about the survey foot because both the l00' tape measures I have are in
survey feet. Messed me up on a home construction project about 13 years back.
It was then I learned there are 2 differing feet definitions.

~~~
function_seven
Are you sure it was the differing length of each version (about 610
nanometers), or was it because your tapes were marked in tenths of a foot
instead of inches?

~~~
jessaustin
I have actually worked with people who didn't notice this about their 100'
tapes. Even better are the tapes divided by 12 on one side and 10 on the
other...

