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Comment by mrguyorama | Hacker News Reader

IMO metric is missing a critical measurement that is roughly the size of "a foot".

Most measurements in one measuring system have very similar equivalents in other measuring systems or useful approximations, like a pound being 1/2 a kilo, a liter being about a quart, or a meter being about a yard. Even various ancient chinese measurements can be similar like this.

Except the metric system seems to have eschewn the common measurement of "About the length of a human foot". It confuses me.

What do you call a footlong submarine sandwich in the metric system? A third-meter-long? A decimeter-long? It wouldn't fit into the power-of-ten based system.

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Imperial measurements are often based on the human body: an inch is the width of a thumb, a yard is the distance between your nose and your outstretched finger, a fathom is outstretched finger to outstretched finger, a mile is a thousand paces, hands are still used to measure horses...

This is great for estimation, but these separate measurements had to be massaged to get them all on the same base (there were three different definitions of the fathom in use well into the 1700s) so the result is somewhat arbitrary (4 inches to a hand, 3 hands to a foot, 6 feet to a fathom, 880 fathoms to a mile). Metric's clearly the more consistent, simpler system for anything beyond estimates.

The closest to what you're looking for is probably the decimetre (dm) at 100mm (roughly one hand). But in everyday speech, "30 centimetres" sounds less clunky than "3 decimetres", and in technical speech everything human-scale is done in mm.

Subway (the fast food chain) calls them "30cm subs", or colloquially "a thirty".

The smaller sandwich is a "15cm sub", or "a fifteen".

It's because inhabitants of metric land neglect the decimeter, probably because it's too awkward of a word.

Define 1 metric hand = 1 decimeter, and you can cleanly convert between hands and meters (it's just a factor of 10 instead of the weird jump from centimeters to meters) and at the same time be able to approximate three metric hands to a foot.

I went to school with a 30cm ruler in the 80s. As a result I have an instinctual sense for that length.

Why shouldn't a measurement that is so natural and familiar to most people that most human societies developed an analogous version and even places without it still end up using it, be a first class citizen of that measurement system?

That's what confuses me. It's a dumb confusion admittedly. It's basically an argument to "Beauty" or aesthetics or similar.

Why do you need feet to measure anything? I've never in my life measured anything using feet. Paces, that's a different story, but those are closer to 1m, anyway.

It's the length of an A4 sheet of paper (also, by extension, the size of many school books, backpacks and … rulers).

In the UK 300 mm is, or at least used to be, referred to as a metric foot.

I lived all of my life in metric countries and I never felt that was missing. One foot is 30cm, two is half a meter, three one meter.

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