The reason it’s so annoying to do conversions between different types of traditional units is because these units were never meant to be converted. Different trades in different places had different traditional measures, and those measures were not the same. If you’re producing wheat you measured it in bushels, if you’re producing beer you measured it in hogshead barrels, and nobody cared how many bushels there were in a hogshead. This is how we have troy ounces and regular ounces and fluid ounces, because those units were used in different industries for different reasons and used different standards.
In any case, there is only one metric standard of time, the second. All other periods of time are either derived empirically (for days and years), or are just named multiples of the second (for minutes and hours). If we based our time on the length of the day or the year we’d have to increase the length of second constantly, because different days and different years are not precisely the same length.
Here you’ve said one important thing: “I like the ones I call ‘useful’ because I usually use them. I don’t like the other ones because I don’t usually use them.”
No, of course that’s not the argument I was trying to make.
Do you agree that, for some purposes, a kilometer is a better (more convenient or more natural) unit of measure than a meter? And that for other purposes, a millimeter is a better unit than a meter?
Well then, I claim that there might be contexts in which a foot or an inch is a better (more convenient or more natural) unit of measure than a meter (or any other metric unit), for similar reasons though not to the same degree.
I don’t know for sure whether there are, and I’m not going to insist on it. But the reason I think there may be is that I suspect the reason feet and inches and such became so widely used in the first place is because the distances/amounts they stand for are convenient and natural.
Only, they weren’t, both because each place that had human-body-based measurements had different ones and because units with the same names were different.
There are contexts where inches are better, and contexts where centimetres are better. Both are arbitrary and unnatural. Well, inches are based on something, and centimetres are based on something, but both of the “somethings” are obscure and irrelevant now. Feet and inches exist because “we need a short measure for small things and a longer measure for longer things, what can we come up with?” There’s nothing natural at all about measuring things, in the first place. It is natural that people wanting to measure things will use whatever they can get that seems reliable, but unless you’re using REAL barleycorns or YOUR OWN thumb or YOUR OWN foot, they’re arbitrary as hell.
Actually, we’ve only gone about 90% metric in Britain. Though we wouldn’t use anything but metric in school, our road signs are still in miles and yards, our beer (and sometimes milk) is still pints, and I’d say most people still use imperial units for anything informal. Height? Feet and inches. Someone’s weight? Stones. Stones are only used as a casual measurement of human weight, but virtually every set of bathroom scales here has them on.
I like quirky old things, but keeping a unit of measurement in use for the sole use of being slightly vague about how chubby you’re getting is just unnecessary. I wish we’d just get it over with.
For me, it’s mental. When someone says they’re six feet tall, I know how tall that is. When someone says the store is three miles away, I know how far that is. But if you tell me someone is a meter tall or something is six kilometers away I have no idea what that means. I can figure it out, but it’s not instinctual, like miles and feet.
To answer the OP, because it’s tremendously useful to society to divide time into segments that everyone agrees with, understands, and uses. Hard to do business or anything without it.
We name days so that we can refer to them. Arguably, we name anything for that reason, although that is not the only reason. We name mathematical concepts so we can refer to them. In Israel, the days of the week are Day 1, Day 2,…, Day 6, Sabbath.
Originally, we divided the day time into 12 hours which started with sunrise. The length of the hours varied during the year. The ninth hour was dinner time and that word eventually evolved into “noon”. The night time was divided into 4 watches, meaning obvious. Also variable length during the year. How and when we decided to also divide the night into 12 hours, make all hours of equal length and start the counting halfway between sunset and sunrise, I don’t know. Time zones started out as “railroad time” and was universally adopted until sometime in the 20th century. My father told me that he recalls the clock tower in Media PA (the county seat of Delaware County, just west of Philly) being three minutes behind the one in Philly city hall. That could have been as late as 1934 since I know my parents married in Media in that year and I cannot imagine any other reason for his going there.
We always use godawful long decimals with metric because you’re supposed to use godawful long decimals with metric.
Consider the meter. Meters are a terrible unit to use to describe the height of a person. They’re too big! “How tall are you?” “A bit less than two meters.” “How about you?” “A bit less than two meters.” “And you?” “A bit less than two meters.”
Now of course you’re going to say that they wouldn’t answer like that; they’d answer with a precise measurement - which is to say, a gawdawful long decimal. Which is also awful - but what choice do you have?
Decimeters, then? Well, aside from the fact that nobody knows what the hell a decimeter is, it’s way too small to be useful for such a measurement. It’s just a few inches long, and nobody knows what seven of those piled up is.
Which kind of highlights the problem of metric - dividing by ten is great for math, but it’s kind of crappy for practical purposes. Ever tried to cut a cake into tenths? How about hundredths? Divided a liter of liquid evenly into its next smaller unit without using a measuring cup? Dividing a gallon of water into two even halves is far easier, and from there quarters is easy as well.
Metric is great for math and science. In practical usage some of the units are of convenient size for some purposes, but others aren’t great, and the numbers don’t work out conveniently - the decimals are always long and godawful. (Or there’s a godawful lot of digits to the left of the decimal; same thing, really).
You’ve never seen a half liter soda at a convenience store? Or a 2 liter bottle?
And 1/3 and 1/4 liter sizes are also common. Well, not in the US but in general.
Just because something is metric doesn’t mean you are magically forced to use powers of 10 and only powers of 10.
Why do you think we have pints and quarts and such in the first place? A gallon is not exactly a convenient unit by itself. So subdivide it (just as we commonly subdivide liters).
And the inch? 1/12 of a foot? Why 12? Ever try dividing something into 12 equal pieces? Why do we say a marathon is 26.2 miles? Why the 0.2 instead of 385 yards? We don’t use ounces to describe a person’s weight. We use decimals there too. The same level of precision can be used in metric just fine.
Of the objections to the metric system, the more common use of decimals is not a sensible one.
As for height, the usual practice is centimeters, which is a perfectly cromulent way to do it, e.g. 192 centimeters, or 1.92m if you want to do it that way. That’s definitely as sensible if not more sensible than 6’ 3" (or 6.25 feet if you want to decimalize).
Well yes, but my point is that 12 is just as arbitrary as 10 and arguably worse in some ways. The idea that it is somehow more “natural” or “convenient” to use it makes no sense. As noted, we can divide a liter by 3 or 4 just fine even before we get to the weird decimalization argument.