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Comment by thechao | Hacker News Reader

The US doesn't use imperial. It uses US customary. US customary uses imperial "prefixes" but is (mostly) base-2. The idea (from the 1790s) was that there'd be a "scientific" system in base-10, suitable for high-precision instrument makers; and, a "human-scale" base-2 suitable for people with limited manufacturing capability: dividing by 2 being far easier than by 10.

Jefferson was responsible for US customary and got a lot of it working; the French were responsible for metric, but were interrupted by The Reign Of Terror.

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> dividing by 2 being far easier than by 10

Really? I struggle to see how dividing any number by two is easier than dividing it by ten, but would like to be enlightened. Divide by ten I just need to mentally move the decimal point, dividing numbers such as 35 or 123 by two requires a lot more mental arithmetic.

It's 1795, and you're a farmer asked to build a ruler based on divide-by-10, or divide-by-2. Anyone with a compass can do the latter; the former is nearly impossible.

Not the number, but the "thing" itself.

It's a snap to fold a piece of paper in half, thirds[0], quarters, sixths, eighths, (etc), but I'm not aware of a trick that lets you divide a sheet into tenths.

[0] Higher powers of three seem tricky too.

could you please explain how US customary is base 2?

For example, how is "12 inches to a foot, 3 foot to a yard, and 1760 yards to a mile" base 2?

My understanding, before reading your post was that US customary was basically adapted from imperial which was in turn just an adaptation of folk measurements - a foot was about the length of a foot, etc.

Lengths aren't as important to farmers as volumes — those are base-2. Remember: 1790, not 1990.

a quart is a quarter of a gallon, an oz is a 32nd of a quart... eh I guess that makes sense.

Sadly, teaspoons to tablespoons has a jump of 3x, but other than that it's mostly binary with a few skips (e.g. there's not a real half gallon unit AFAIK, it's just "a half gallon", same for 2 fl oz). For some reason a barrel is 31.5 gallons instead of 32, with a hogshead being twice that at 63, but those are pretty rarely used.

I guess they are referring to how inches for example are commonly subdivided into halves, quarters, eighths, sixteenths, etc.

> dividing by 2 being far easier than by 10

How is dividing by 2 easier than moving the decimal point by 1 place?

Fold a piece of paper in half perfectly. Easy

Fold a piece of paper into 10 equal parts perfectly. Easy?

I think they meant literally dividing, as in "divide this loaf of bread into two equal parts".

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