bagpiper wrote:However, in construction, the imperial system has some significant advantages. A foot can be divided by 2, 3, 4, and 6 without having to drop into fractional/decimal measurements.
Meh. Power of 10 units can always be divided easily by 2, 4, 5, 10, etc. Power-of-10 units are a little less convenient if you often need to divide by threes, but that's the only place where 12s are better, and 12s suck if you need to divide by 5s. Plus, for example, in construction, where thirds are useful sizes are often chosen to have a multiple of 3 in them -- for example, a standard metric door frame size is 900 mm x 2100 mm. You can divide those easily by 2, 3, 4, 5, 6, 9, 10... much easier to divide than a 36 inch x 80 inch frame.
And imperial really sucks when you start getting down to things that are fractions of the smallest common unit. Is 3/8" bigger or smaller than 5/16"? No, it's not hard, but you either have to just know it or you have to do some trivial fraction math. Is 15mm bigger or smaller than 12mm? A four year-old can tell you that.
bagpiper wrote:An acre foot of water has immediate and tangible visualizations for anyone dealing with irrigating crops or even storing water whereas I suspect that 1233 cubic meters of water is merely a meaningless abstraction to everyone who doesn't mentally convert to "about 15 centimeters deep over a hectares".
Umm, people irrigating crops or storing water wouldn't think about 1233 m^3, or ~15 centimeters over a hectare, they'd think about 1000 m^3, which is very nicely visualized as a cube of water 10 meters on a side (for storage) or 10 cm over a hectare (for irrigation). And notice how much nicer it is if you have to figure out how much storage volume you need to store your 10 cm per hectare. Tell me off the top of your head how large a storage tank you need for one acre foot.
And while tenths of a degree are fine for lab use, most of us find them annoying at least for use in real life so the small interval of Fahrenheit degrees over centigrade or Kelvin (sure, let's all get used to water freezing at 273.15k and a typical room temperature of ~295k
) offers the advantage that most daily temperatures can be adequately expressed without the need for any decimal degrees.
People who use centigrade for daily temperatures don't feel the need to use decimals. I'd argue that the Fahrenheit scale is overly precise for that sort of use anyway... how often is it important to distinguish between 81 and 82 degrees? Centigrade basically has one degree for every two of Fahrenheit, which is perfectly adequate for non-scientific purposes.
bagpiper wrote:the fact that the imperial system was/is based on units derived from daily experience means it is more than just bigotries of first exposure that make the units of the imperial system easy to visualize and apply.
No, it's just experience. People who use SI units on a daily basis find them just as easy to visualize and apply. It's not like human feet are really very close to one foot in length, or that a gallon or a cup actually corresponds to any common physical object's volume, or that there's any very standard object that weighs a pound.
bagpiper wrote:A gallon, quart, and cup work great in the kitchen and so they get used.
Liters and deciliters work just as well. Actually, SI-unit recipes tend to use 100 ml (~1/2 cup) as the basic conceptual unit, and then use multiples, halves, quarters, etc of that. And they have the advantage that when they go down to quantities much smaller than a cup, they can continue using ml, going down to 10 ml, or 5, etc. In Imperial units you have to switch to tablespoons and teaspoons. How many teaspoons are there in 1/16th of a cup? (3, obviously).
bagpiper wrote:Acre-feet work great in the field.
But cubic meters work even better in the field, as I pointed out above. If your ditch is 100 yards long, 3 feet wide and 2 feet deep, and it's full, but the gate was just dropped so no more will flow in, how many acre feet is waiting there to drain onto your field? With SI units you can do it in your head (granted that most people wouldn't care -- but how much of that is because it's just too hard to work out in Imperial units?).
bagpiper wrote:Rarely do we need to convert from kitchen to field and so there is little need to use a single system in both kitchen and field.
But neither is there any disadvantage to using a single set of units for both, and when you do need to convert using two different sets, with oddball conversion factors between them, it sucks. It sucks so much that people often don't try, and it often doesn't even occur to them to try to estimate when it might be useful.
Also, you're underestimating the utility of easy conversions, especially between spatial volume, liquid volume and weight, and not just "in the lab".
When I fill the 150-gallon water tank on my trailer, how much weight does that add? I happen to know that water weighs about 8.33 pounds per gallon, so I can do the multiplication and determine that it is about 1250 pounds. But if my water tank were 600 liters, I'd know that it weighs 600 kilograms.
Even better, what if I didn't know what the liquid volume of the tank was and just had to eyeball it? How would I estimate how many gallons of water a tank 8 feet long by 3 feet wide by 10 inches deep can hold? I happen to know that a gallon is 231 cubic inches, so I can grab my calculator or a pencil and piece of paper and compute 96*36*10/231 = 150 gallons, then I can multiply by 8.33 to get the weight.
But with SI units I'd see that the tank is about 2.5 m long by 1 m wide by .25 m deep so 2.5*1*.25 = 0.625 m^3 (a multiplication I can do in my head, BTW, since I know that 25 * 25 = 625). So it holds 625 l, weighing 625 kg. No calculator required, and no memory of weird pounds or cubic inches per gallon conversion factors.
That's just an example that came to mind because I did it last week.
bagpiper wrote:Where we do a lot of conversions (lab, classroom, etc) the SI system clearly reigns supreme over the Imperial system. But that doesn't mean SI is "the best" system in other settings.
The SI system clearly reigns supreme when there are a lot of conversions to do, and it's just as good as the Imperial system when there aren't a lot of conversions to do.
So, yes, it is the best system in nearly all settings. I put the "nearly" in there only because there's probably some obscure situation that can be contrived in which SI has a minor disadvantage. Heck if I can think of one, though.
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