4 ms·

Can’t talk to the statute mile, but the nautical mile is sublime: one minute of latitude. The amount of math you can do in your head with a system with so many

Can’t talk to the statute mile, but the nautical mile is sublime: one minute of latitude. The amount of math you can do in your head with a system with so many factors of 2, 3, and 5 is truly amazing.

mulmen 6y ago
I'm not aware of any tricks to make mile calculations easier but the fractional scale common with the inch is very useful for real-world mental calculation and practical exchange. Effectively everything is powers of two. Got something between 1/4 and 1/2 inch? Great, use 1/8ths. It's three. Not close enough? How about five 16ths? It infinitely scales to provide another unit that is suited to the measurement at hand. In some contexts you might just say you pick the closest 1/8th. In others you might use 32nds. You can use the same measuring devices to agree on an ad-hoc standard that everyone understands. But with the metric system you only really get cm (too coarse) and mm (too fine) but you don't get something like 9/16 so you can't "work in 16ths" and have everything be whole units again. Adjusting HVAC in degrees-C is infuriating to my Fahrenheit sensibilities. 20C is cold, 22C is hot. 21C is probably ok but really I want something like 20.5C. The comfortable range for a room is 3-5 whole units of F, but requires a bunch of fractions in C that you may not even have available on your thermostat. Sure, converting between units is easy in the metric system. That doesn't make it the best thing to use all the time. Hell, the idea of thousandths of an inch is used commonly, so even the imperial system is base 1000 in some cases. But I've never seen anyone utilize the fractional scale with metric units, probably because the units are the wrong size for that to be useful.
- onion2k 6y ago
  But with the metric system you only really get cm (too coarse) and mm (too fine) but you don't get something like 9/16 so you can't "work in 16ths" and have everything be whole units again. People who use metric units are perfectly happy rounding to the nearest 0.5cm or 0.25cm if that's what's needed, exactly as people do with inches. Why on earth would you imagine people use mm if something doesn't call for them?
  - mulmen 6y ago
    But does anyone say 1/8th centimeter? Seems easier to just drop down to millimeters at that point. Which is fine, but it loses out on the convenience of fractions.
    - onion2k 6y ago
      People do say things like 1.25mm, which is 1/8th of 1 cm. Presumably someone who uses Imperial would say 5/128th inches if they wanted to describe something that's equivalent to 1mm?
      - Evidlo 6y ago
        Most likely they would use mils/thou. 25mils ~ 1mm Or 1/16in as others have said.
        Hextinium 6y ago
        40 mils ~ 1 mm 1000 mils / 25.4 mm = 39.3 This simple fact still seems wrong to me somehow.
        Evidlo 6y ago
        Brain fart
danaliv 6y ago
Also the average of one minute of arc on a great circle route, which was the real handy thing about it at sea.
- killjoywashere 6y ago
  Yes, meridians (on which latitude is measured) being a special case of great circle routes that happen to pass through the poles. That said, as a practical matter, you are more frequently contemplating a chart of smaller scale than "globe" so you're usually counting up distance between fixes, or distance to next turn in a harbor, or some such thing, where you have a compass in hand and just need to set the compass to the length of a mile. The nearest latitude tick marks are quite handy for that.

mulmen 6y ago

I'm not aware of any tricks to make mile calculations easier but the fractional scale common with the inch is very useful for real-world mental calculation and practical exchange. Effectively everything is powers of two. Got something between 1/4 and 1/2 inch? Great, use 1/8ths. It's three. Not close enough? How about five 16ths? It infinitely scales to provide another unit that is suited to the measurement at hand. In some contexts you might just say you pick the closest 1/8th. In others you might use 32nds. You can use the same measuring devices to agree on an ad-hoc standard that everyone understands. But with the metric system you only really get cm (too coarse) and mm (too fine) but you don't get something like 9/16 so you can't "work in 16ths" and have everything be whole units again. Adjusting HVAC in degrees-C is infuriating to my Fahrenheit sensibilities. 20C is cold, 22C is hot. 21C is probably ok but really I want something like 20.5C. The comfortable range for a room is 3-5 whole units of F, but requires a bunch of fractions in C that you may not even have available on your thermostat. Sure, converting between units is easy in the metric system. That doesn't make it the best thing to use all the time. Hell, the idea of thousandths of an inch is used commonly, so even the imperial system is base 1000 in some cases. But I've never seen anyone utilize the fractional scale with metric units, probably because the units are the wrong size for that to be useful.

onion2k 6y ago
But with the metric system you only really get cm (too coarse) and mm (too fine) but you don't get something like 9/16 so you can't "work in 16ths" and have everything be whole units again. People who use metric units are perfectly happy rounding to the nearest 0.5cm or 0.25cm if that's what's needed, exactly as people do with inches. Why on earth would you imagine people use mm if something doesn't call for them?
- mulmen 6y ago
  But does anyone say 1/8th centimeter? Seems easier to just drop down to millimeters at that point. Which is fine, but it loses out on the convenience of fractions.
  - onion2k 6y ago
    People do say things like 1.25mm, which is 1/8th of 1 cm. Presumably someone who uses Imperial would say 5/128th inches if they wanted to describe something that's equivalent to 1mm?
    - Evidlo 6y ago
      Most likely they would use mils/thou. 25mils ~ 1mm Or 1/16in as others have said.
      - Hextinium 6y ago
        40 mils ~ 1 mm 1000 mils / 25.4 mm = 39.3 This simple fact still seems wrong to me somehow.
        Evidlo 6y ago
        Brain fart

danaliv 6y ago

Also the average of one minute of arc on a great circle route, which was the real handy thing about it at sea.

killjoywashere 6y ago
Yes, meridians (on which latitude is measured) being a special case of great circle routes that happen to pass through the poles. That said, as a practical matter, you are more frequently contemplating a chart of smaller scale than "globe" so you're usually counting up distance between fixes, or distance to next turn in a harbor, or some such thing, where you have a compass in hand and just need to set the compass to the length of a mile. The nearest latitude tick marks are quite handy for that.