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Which is why some branches of physics use "natural" units - the speed of light == 1, etc.
Freedom is the freedom to say that two plus two make four. If that is granted, all else follows.
-- 6079 Smith W.
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Units are an attempt to codify something physical into a value. For things that people use every day in casual life, the best units are those that are easily visualized or understood. This is because those same people will whine in school about having to take geometry or trigonometry and then get bamboozled by a contractor because they didn't know how to do math. Making units easily quantified by things in every day use and you won't end up with a building that was built for you at half scale. In designing trajectories in the solar system, I use astronaumical units (AU) more than any other unit of distance except when performing a flyby, in which case I wouldn't care if I measured the altitude in km or mi or even nmi, but am usually dictated to use km.
Fahrenheit is useful for describing human comfort. It expands the scale where humans live. Much below zero degrees F really sucks even with extra clothing and just breathing in starts to hurt. Much above 100 degrees also really sucks as you can't shuck many extra clothes to feel comfortable. A foot is about the length of an adults foot, which makes it easy to walk off a distance. Pounds make no sense. Many imperial units are easy to estimate by using the human body, which is how a lot of imperial units came to being. They don't make doing math problems in physics easy. MPH isn't particularly relatable when driving a car and you just have to calibrate it, but neither is kph.
Because I've converted it enough I know that 40 degrees C sucks and I know that somewhere -20 degrees C also sucks. However, that really is only 60 degrees C of describing comfort. There is a big difference in an 80 degree F day and a 60 degree F day. Even between 72 degree F and 78 degree F you can easily feel the difference in comfort. A better unit for measuring human comfort would probably center around 72F with positive numbers being warmer than optimum comfort and negative numbers being colder than optimum comfort and be about the size of a degree F but maybe a little bigger. C is useful for cooking since 100C is the boiling point of water at sea level, but since a lot of the world is above sea level even that isn't super useful, but better than a random number like 212F. A meter isn't particularly useful at measuring things in the casual life of a human other than saying that human adults are typically between 1.5 and 2 meters tall. Grams don't make a lot of sense and you have to raise it to a kilogram to be useful to visualize in human life.
PSI is pretty useless, but so is pascals.
If people stress that you should consider domain specific languages, those same people should stop trying to make everyone use the same units for every domain. Also sometimes Fortran REALLY IS one of the better options.
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firegryphon wrote: Also sometimes Fortran REALLY IS one of the better options.
 In my early time as a contractor I wrote a Fortran program to produce my bills.
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A few years ago I was writing a model importer for GIS data (geographic information systems), and that turned out to be an education in measurement systems. Prior to that, I thought that the USA had, in a sense, already "gone metric" since 1 foot is defined as precisely 0.3048 meters. That's not a rounded-off approximation, that's a precise definition.
But it turns out that that's merely the "international foot." In contrast, the "US survey foot" is defined as precisely 12/39.37 meters (1 US survey inch defined as precisely 1/39.37 meters). The conversion factors are almost but not quite equal, and the differences accumulate when measuring the Earth.
There are several other definitions of "foot" around the world.
The other things I learned (I knew them before, but then I learned them) are:
1) The Earth isn't a sphere; it's an ellipsoid.
2) The Earth isn't an ellipsoid; it's a geoid.
3) Latitude is defined by the normal vector at the surface, not the central vector to the surface.
4) Double-precision coordinates are essential everywhere.
5) Defining a meter as a precise fraction of the distance between the equator and a pole was bound to fail at some point.
6) We're still left with arbitrary-looking conversion factors from "natural units" (such as the speed of light) to MKS units (meters and seconds) -- but with many more digits due to the greater precision.
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I disagree.
That would be like discarding Google in favour of old fashioned printed books...
OOOPS! 
"In testa che avete, Signor di Ceprano?"
-- Rigoletto
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I know what you mean, I cannot visualise things in metric sizes I have to convert them mentally to feet and inches ( or whatever ), metric can be ambiguous to, some people say ( usually related to the building trade ) you need a 60*40 or a 600*400 - there is no ambiguity in you need something 2 foot by three foot.
"I didn't mention the bats - he'd see them soon enough" - Hunter S Thompson - RIP
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I live in Canada and have been using metric since grade school. That being said, I still buy 2x4's for framing, and sheets of plywood come in 4x8 sheets. The crazy thing is that our plywood is often 4x8 sheet by 5mm.
Outside of a dog, a book is a man's best friend; inside of a dog, it's too dark to read. -- Groucho Marx
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You can visualize imperial units because you grew up with them. If you used metric all the time you'd be able to visualize it quickly enough.
If you dropped the units on your 2x3 like you did on your metric measurements then you'd be just as confused (is that 2"x3" or 2'x3'? And yes, I have run into just this problem when ordering materials online.) The solution is don't drop the units! (Make it 60cmx40cm or 600mmx400mm)
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I'm a 65 year old English engineer who was brought up on imperial and worked to it for many years - and its critics today simply don't understand the way that it was used! My first job in the real world was as a turner - manufacturing drive shafts for relatively large turbines on a lathe. All our engineering drawings were in imperial measurements - but that did not mean yards, feet, inches and eighths of an inch. The drawing I worked to told me that the shaft should be 103.5 inches long, 6.35 inches diameter and I should put a 5 thousandths of an inch chamfer on each edge. As a check after it came out of the lathe, I would weigh it and the specifications told me that the answer should be 537.88 ounces.
Yes, the original definition of imperial measurements was pretty arcane - but it was not used that way for serious things. We used it as a metricated system with different basic units to the SI system. And I would say, as an aside, that the imperial units are more pragmatic than the metric ones. They were based on every-day life whereas the metric system was driven by the French who tend to like to base their systems on some academic and philosophical structure. Metric units tend to be too big or too small for pragmatic usage - if I'm measuring the width of a worktop or the diameter of a screw, I really don't give a damn whether or not the unit I'm using is some full decimal fraction of the circumference of the earth or the distance between the earth and the sun! If I'm ordering a glass of beer, I want to receive a quantity that is comfortable to lift but large enough that I'm not going to have to order another within the next few minutes!
Martin
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I hope you're aware that metric time isn't dd/mm/yyyy nor ISO8601 or similar.
In the original metric system, 250 or so years ago, a week was ten days. And every day was divided into decidays and centidays.
This (luckily?) didn't catch on.
But in 1954 when they created the SI-system they settled for the second as a base for time.
So metric time is measured in decasecond, hectosecond, kilosecond or megasecond or gigasecond.
I prefer ISO8601! 
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Was that before or after the shift from days starting at Noon and running overnight? 
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Canada is metric. That's why all temperatures are in F, weights in lb and heights in feet and inches.
cheers
Chris Maunder
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Canada must have "New Metric" 
Get me coffee and no one gets hurt!
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... and we buy plywood in 4'x8' x 5.0mm sheets.
Outside of a dog, a book is a man's best friend; inside of a dog, it's too dark to read. -- Groucho Marx
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I think my favourite over here is Tirecentre.
Talk about culture collision.
cheers
Chris Maunder
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Why don't we just go back to the old units of measurement? We still measure horses in hands. Drinks are measured out in fingers. We should bring back the ell, the cubit, the palm and the digits. Add to that the carucate, the hide, the oxgang, the virgate, the yardland, and the quinaria.
Do people still use the barleycorn for measuring shoe sizes?
How about the lachter or the button?
Don't forget the line, the page, the rod, the step, and the stadion.
I think weights are still sometimes measured in bags, are they not? The Dutch cask is used for measuring butter and cheese, I think. How about the duella, the keel, the lot, the mark, the pennyweight, the roll, the room, the sarpler, the slug, the tod, the truss, and the whey.
I could go on and on (and on and on and on) but I think I've put just about everyone asleep by now.
The point is, if you are going to be sending code or data where it may need to be read by other cultures, either choose an international standard, or just document what standard you are using and let the user use their brain (or a calculator) from there. standards of time and measurement come and go. Some stay longer than others. All have their advantages and disadvantages. It all depends on the context of its use, and the primary audience.
Money makes the world go round ... but documentation moves the money.
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That would be really nice, but over the years I've found that the bigger problem is systems using different units within the same environment, even though all are metric. E. g. in construction industry, measurements are typically given in mm, except for some that are, by some unwritten law, always presented in cm, and a few in meters (meters above sea level to be concise).
Woe to the CAD software programmer who needs to process data based on such measurements without concise information where they're coming from!  But I guess it's even worse for programmers in the U.S. ... 
GOTOs are a bit like wire coat hangers: they tend to breed in the darkness, such that where there once were few, eventually there are many, and the program's architecture collapses beneath them. (Fran Poretto)
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Maybe we could get everyone to drive on the proper side of the road too. i.e. the left. 
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5teveH wrote: Maybe we could get everyone to drive on the proper side of the road too. i.e. the left middle.
FTFY 
Freedom is the freedom to say that two plus two make four. If that is granted, all else follows.
-- 6079 Smith W.
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But ... the majority of cars I see *are* driving on the left side! And that's for the better, because those are the ones heading my way! 
GOTOs are a bit like wire coat hangers: they tend to breed in the darkness, such that where there once were few, eventually there are many, and the program's architecture collapses beneath them. (Fran Poretto)
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As long as they will be things like national pride, country specific formats, as dumb as they may be, will not disappear.
It will probably take decades to get rid of mm/dd/yyyy (which, while I understand the write-it-as-you-speak-it, has overall more disadvantages than advantages)
It will take centuries to settle for imperial or metric ( I prefer metric because more straight forward to me, but I don't care as long as we settle for something)
Flying cars is probably the only way of getting everybody to use the same side of the road for driving, and I am not even convinced about that. Maybe this will not be an issue anymore with autonomous driving.( You would not imagine what a waste of resources and time developing a left hand drive and right hand drive version of a car is).
This, as well as many other things, would have been solved a long time ago if people had common sense. But ...
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Rage wrote: You would not imagine what a waste of resources and time developing a left hand drive and right hand drive version of a car is
The car needs to be able to do both; and it should know where to switch. There's people coming from England using the canal; if their cars only can drive left, you'd get very dangerous holidays and visits.
Bastard Programmer from Hell 
"If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.
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Quote: write-it-as-you-speak-it
What about the 4th of July? Were Americans saying dd/mm/yyyy before but switched at some point, but "the 4th of July" stayed as is?
Also it doesn't really make sense to me to start with month, then day, then year. Either go from less specific to more or the other way around, but don't mix them up.
What time is it? It's 7 minutes, 35 seconds, 4 hours.
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Riz Thon wrote: it doesn't really make sense to me to start with month, then day, then year
Me neither, but the write it as you speak was the argument brought here last time this was raised as a point in the Lounge
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But today is 07/04/2021 - It says so on my task bar. Not a celebration?
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