[nwiswell]

Why does the foot being divisible by 12 help anything? If you're dealing with something 7.3 ft long, what's the advantage over 2.23 meters?

Hell, if you've got something 2.4 meters long and 7.87 ft long, it's the metric length that happens to be conveniently divisible by 12.

The situation with machine tools in the US is unbelievable, by the way. So many stupid mistakes have been caused by the confusion between mils (1/1000 of an inch) and millimeters. And many many tools and bits are designated in fractional inches rather than whole or decimal units (as in countries using metric) which is a massive pain in the ass because both CAD software and quick mental comparisons are generally not conducive to bizarre fractions like 9/64".

The situation is legitimately a little bit different with minutes and hours, since we are able to specify units of time somewhat arbitrarily to match the units, i.e., if hours were 64 minutes instead of 60, many meetings would instead be 64 (or 32) minutes long. This has to do with the reality that we generally do not know accurately in advance exactly how much time is required, so in general there's a lot more approximation involved with common measures of time than common measures of distance, and it's handy to be able to split the hour cleanly in multiple ways.

[explaininjs]

Carpentry and construction are both also areas where you don't really have an "exact" need to be at certain measure. You can usually get away pretty well with just picking a nice round number and going from there.

Machining is different, and metric is accordingly often used there.

[rrr_oh_man]

> Carpentry and construction are both also areas where you don't really have an "exact" need to be at certain measure. You can usually get away pretty well with just picking a nice round number and going from there.

This does not sound like you’ve done much of either. I spent my summer rebuilding my kitchen and, oh boy, do millimetres matter.

[lolinder]

> The situation with machine tools in the US is unbelievable, by the way. So many stupid mistakes have been caused by the confusion between mils (1/1000 of an inch) and millimeters.

To be fair, this wouldn't be an issue if we had only imperial units. It's only possible to mix these up because we have an awkward mix of both systems.

> The situation is legitimately a little bit different with minutes and hours, since we are able to specify units of time somewhat arbitrarily to match the units, i.e., if hours were 64 minutes instead of 60, many meetings would instead be 64 (or 32) minutes long.

The same situation is true of carpentry, though. when we're building something out of wood we rarely have specific dimensions we must meet, we're building something artificial and can pick the closest round number. 2x4s are 2" by 4" not because they need to be slotted into some naturally-occurring fixture but because it's a nice round number that is sufficiently useful. The standard ceiling height in the US is 8' not because of any law of the universe but because it's a round number that's easy to measure and easy to divide (quarters, halves).

Your examples of something 7.3 feet long or 7.87 feet long simply don't come up in carpentry because we'd usually just round up to a nice number and scale the whole project accordingly. And if we do have something that needs to be precise within +/- a certain tolerance, a base unit that is easily divisible is more likely to be able to round conveniently while remaining within the tolerance.

[kelnos]

Ugh, so I was just making some new window screen frames to replace some that were missing, and what a pain that was to measure things out. I had fun dimensions like 21-5/16" all over the place. Now, they certainly didn't need to be accurate to a sixteenth-inch, but being off by even a quarter inch could easily make them not fit.

Too large and you just can't get the screen into the frame, and too small and it can just fall out, or at the very least leave gaps large enough that bugs can get through.

I agree with you that there are many things where we don't have a specific physical need for certain dimensions, so we just pick round numbers. But I think the cases where we do have to conform to some messy existing physical dimensions come up more frequently than you think.