That is indeed one sense of the word factoid, but in common North American usage it also can mean “small or trivial piece of information”, which is the sense I believe the parent poster is using.

That's fine for measuring most things, but not necessarily for survey work. Your reference points can be quite far away, and you are dealing with angles. So ever pretty tiny changes can be significant.

Johansson rounded the inches, but previous legal definition was in yards. The Mendenhall Order was the US agreeing to define it's units in terms of the metric pegs, instead of the UK's (which were unreliably changing). The US survey of the coast (today the national geodetic survey), defined conversion values for the yard and pound.

1 (survey) yard = 3600⁄3937 meters

Reduces to:

1 (survey) foot = 1200⁄3937 meters

1 (survey) inch = 1/39.37 meters ~ 25.4000508 mm

https://en.m.wikipedia.org/wiki/Mendenhall_Order

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

That's a lot closer! argh!

The left ones.

Sorry, I'll show myself out.

The non-survey one

What would the cost be to change everything for a country the size of the USA? I imagine it would be in the trillions.

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

It's entirely possible that they might not be aware. Surveyors are concerned with measuring bearing and distance from an arbitrary location (5000,5000) in some cases. The distances they traverse are not enough to see differences between US Survey foot and Int'l Feet. Cartographers and GIS folks who tie into a photogrammetric basemap are probably more aware. Most Civil engineers are like 'NAD83? Ok, whatever you say~!'

> The boiling point of water may not be useful on a day-to-day basis, but the freezing point certainly is

The freezing point of water is interesting, but in practice it is pretty variable depending on what adulterants are mixed with it.

Realistically, any day that it gets up to the 20s F you will get some amount of snow melt.

Any time it is above ~0F the roads will de-ice during the day from the salt they put down.

I don't have any issue with people preferring C to F, but I think any choices come mainly down to what you have been exposed to.

My main point is that Fahrenheit is a very practical temperature scale.

> I think you underestimate the usefulness of powers of 10

Powers of ten are just scientific / engineering notation, they aren't really all that dependent on the underlying base units.

The fact that people gravitate toward the measurement system they were first exposed to suggests that they are both adequate in practice.

0deg F was originally set as the freezing point of sea ice, which could be recreated in the lab using a mixture that's more thermally stable than the freezing point of fresh water.

Not as arbitrary as people think. Most units have a good reason for their definition, in the context for which they're used, and are divisible by numbers that are convenient.

Without needing decimals at all.

And in my experience, the people who benefit from base 10 metric are the same people who misplace decimal points.

No the difference is that we process wood now. Look up dimensional lumber. Its confusing, but makes sense if looked at historically. Iy is not shrinkflation or any other such nonsense.

While i don't doubt they're cheating it a bit, the dimensions originally refered to rough cut, pre-dried lumber. Most of the difference came from finish cuts and drying.

Here in NZ when we switched to metric nothing changed, 2x4s (well we call the 4x2s) were never quite 2x4, and 50x100s (the metric replacement) are close enough (but still not quite) that nothing really changed

2 * 4 = 8 so the last significant digit should be an ‘8’

That's why you pick highly composite numbers to create your object. 'Quick, what's 1/3 of 12 meters?' Why do they make raised floors 600mm tiles?

Oh, you rounded. Got it. ;)

Fractional lengths in the US are commonly in base-2, ie, 1/2", 1/4", 1/8", 1/16", etc. Still annoying to remember that the next socket up from 1/2" is 9/16".

At this point one has to point out that US gallons (and pints and cups and flu ounces) are different from the gallons/pints/cups/flu ounces used everywhere else on the planet (for reasons that mostly have to do with English kings trying to get around the parliament's limits on taxation they made some gallons smaller, the US standardised on one of the smaller ones) - fortunately most of the rest of us have stopped using those units so we don't care as much, but we do have to have to be careful with, for example, US recipes.

When visiting Starbucks I'm often tempted to ask the person behind the register "Venti? that's Italian for 20 right? 20 what?" they invariably will say "20 fluid ounces" .... of course the correct comeback is "I'm pretty sure they use the metric system in Italy, it must be litres, or maybe mililitres" - usually they will choose "litres"

That gives you a gallon of exactly 4 liters (256 * 2.5^3 = 4000 mL). Alternatively, a quart is now just another name for a liter.

Added binary teaspoon and dessert spoon, also renaming a few units:

    tspn
    dspn
    tbspn
    oz
    jill
    gill
    cup
    bottle
    quart
    half
    gallon
    peck
    jimmyjohn
    bushel
    rundlet
    barrel
    hogshead
    butt
    tun

There's a ppm error there as well, but that's a usually a different problem. If different units were used, it would be obvious when checking in on the benchmark.

If it's in northing and easting, the baselines are to the South and West of all coordinates covered by the projection, plus an offset. So it might start at 1000000 instead of zero, to ensure format consistency and to catch blunders.

So it's about 2ppm, multiplied by the number of feet between you and the Southern or Western most edge of your state (if single projection state) plus 10^5 or 10^6 or similar.

It's designed to make an error large enough to notice.

Vertical however is rarely a problem, as it's all based off local benchmarks.

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"

Yeah, woodworking is so much easier when using feet and inches. It's so incredibly useful to be able to divide a foot into half, thirds, quarters, sixths, and twelfths.

Well, architectural construction is based on the "octameter", so 12.5 cm.

That adds pretty well ;)

Thanks for the update; I would not have found that!

I once tried to imagine a metric time system, with a deciday of 14.4 minutes. I realized that it would never catch on, because a half-hour TV show would have to be cut to 28.8 minutes losing at least 2 commercials.

I suppose it depends on what your goals are; despite being officially metric, my Canadian and British friends still seem to exhibit a melange of imperial and metric in everyday life.

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.

What’s so special about thirds, sixths or twelfths?

10cm = 100mm; 100mm can easily be divided by 2, 4, 5, 8 (=12.5), 10, 20, 25, ...

That’s a nice thing about metric. If you don’t like the units you can multiply them

I remember when we built our holiday home - yelling out the lengths of dwangs in millimeters - they were perfect for the job, we never needed to divide them in 3

This is also just an anecdote, but I'll second thomk's opinion on woodwork/manual measurement of most kinds. Twelve has one, two, three, four, six, and twelve for divisors, and that is incredibly handy when you're trying to do manual measurement. Even sixteen has one, two, four, eight, and sixteen, making for easier division of pounds to even numbers of ounces; compare this to ten, which has only one, two, five, and ten. People can't eyeball or measure tenths or fifths nearly so easily as thirds and fourths. Even eights are easy to get from measuring a quarter and taking half; good luck eyeballing a fifth. And before all the "we have computers to do it for us" people come out of the woodwork: 1. Not always and 2. High-precision floating-point arithmetic is still computationally expensive and often hard to get right. I think every one has, at one point or another, hit some weird numerical glitch due to floating-point error.

Every schoolboy learns basic unit conversion; I'm not convinced by your tales of hapless relations. It's not that hard to remember eight fluid ounces per cup. It's not that hard to multiply the feet times twelve, add the inches, and divide by twelve to get just feet. It's not that hard to divide the ounces by sixteen to get pounds and ounces. It's not hard to remember that water freezes at thirty-two degrees. I've also never heard someone describe weights as "six pound five" with either meaning; the closest I've heard are descriptions of height as, say, "six foot two". This means six feet and two inches in every case, and everyone understands this.

At this point,

In conclusion, it is sometimes easier. It's just comical to see someone trying to argue that there are literally zero cases where the customary system is sometimes easier.

> My wife's family, who almost all have university degrees

Honestly, this is probably part of the problem.

If you ask the AP Calculus student to calculate these things, they probably don't have that down solid.

If you ask the sweathog vocational tech kid, they will know what the units of measure are and have no problem.

Practice makes perfect.

I once worked with a guy who had just bought a surplus cylindrical water tank, and wanted to get an idea of what it would weigh when filled. I asked him for the dimensions and multiplied each by 2.5 to convert to approximately centimeters. Then I multiplied the diameter by 3, approximating pi. I converted each to the nearest power of 2 so I could multiply by adding the exponents. Assuming 1 cubic cm of water is 1 gram, I had the log2 weight in grams. Then I subtracted 10 to divide by 1024, getting approximate kilograms. Then added 1 to get approximate pounds. Finally took 2 to the power of the result. By the time he finished telling me the dimensions, I had an answer for him.

> 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.

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.

Do most people know 62.4 lb/ft³?

The equivalent metric factor is 1 g/cm³ or 1 kg/L [1] so with D and H in centimeters the calculation is

  π D²/4 × H

kilograms of water.

[1] Assuming we're talking about a normal water tank, not a space rocket. Density varies with temperature, it's 0.9970474 g/cm³ at 25 °C.

> In metric, the weight of water in grams is equal to the volume in cubic centimeters, by definition.

Just to clarify this is not exactly true. It was the original idea, but pretty quickly they realized that it wasn't a practical definition and kilogram ended up being defined by a standard reference object which was carefully stored in a vault in Paris and thus being disconnected from the meter and the density of water. Finally in 2019 kilogram was redefined again in terms of natural constants in the great SI unit upheaval. Although sadly the new definition is not very intuitive to understand.