Yes, it’s from a book called “Uncle John’s Bathroom Reader” and that book was resting on a closed toilet seat in a nation that only kind of uses the metric system in certain situations… however, you’d be surprised how much you can learn after a single visit to any local fast-food joint!
The metric prefix system is a fantastic invention, akin to the arabic number system. Honestly it’s surprising no one came up with it sooner… but (and I’m sure I’ll catch some flak for this) the metre is an awkward length - it’s too big for human scale measurements. The decimetre is not as bad but still not very good, and it’s also not commonly used. The centimetre has the opposite problem - it’s too small for the human scale but too big for precision work.
Don’t get me wrong, the horrible conversions between imperial units make the system unusable for me, but the unit lengths themselves are scaled to humans because they weren’t initially defined arbitrarily by some committee (why should the distance from the pole to the equator be used as the baseline for a measurement used by humans?). I think the inch and foot are great lengths to use on a daily basis, they feel quite natural.
What annoys me the most is that we could have had the best of both, since the foot and inch are only a factor of 12 apart, so we could have had a metre measuring about one foot and a decimetre measuring about an inch.
What? The whole idea of the prefix system is that it’s granular enough that you can describe any size as up to 100s (or 10s of common sizes) of any prefix.
Think of it as scales: Metres is the unit for things people sized (including kids), decimeters for things hand sized, centimeters for grit sized, etc.
Other scales are mostly an extension of the system: Kilometers is “away” sized, millimeters are tiny sized, and following the convention of 10s makes for easy to remember and translate conversions, although I’ll admit that they aren’t inherently more convenient than other measures.
Similarily: foot is stick sized, an inch is pebble sized, but the imperial system then doesn’t easily convert between other common human experiences. Talking of things seed sized becomes weird fractional math, figuring out how many steps it is to the next town (miles I’d argue is “trip” sized) gets weird. And when you need higher precision you end up in fractions of a larger unit rather than convenient ones.
The size of an atom is about 100 pikometers (10e-12 metres) and a molecule about a nanometer (10x the size). In US customary an atom is about 1/262144 (2^18) thou of an inch, and molecules about 1/2048 (2^11) thou of an inch. And if we want it compared to miles or feet, we’ll have to redo the calculations from scratch with loads of danger of messing up conversion numbers.
Besides, most of the benefit of the metric system is that the standardised scale prefixes makes it very easy to correlate all other physical constants. Speed of light is just under 300 km/s, which is about 300 m/ms or 300 mm/ns, or 200 miles/second which is about 1000 ft/ms or 10 in/ns (not to mention that rounding errors are larger in customary)
EtA: I do wish we had a base 12 math system though
For both philosophical and scientific reasons, they wanted a definition that could be recreated any where in the world, certainly not the thumb or foot of any one man. With the “distance from pole to equator” definition, you just need to measure a long north-south axis (say a few hundreds km), and knowledge about the figure of the Earth helps you scale that to the full definition. You can do that anywhere on Earth.
Another considered definition was the length of a pendulum whose half period is 1s, but even at the time the effect of local gravity was deemed to be too much
That’s not the point I’m trying to make. You can derive a length from any number of physical constants to make it reproducible, but considering the divisor of exactly ten million suggests the metric committee were far more interested in making something ‘clean’ than something human-friendly. They could have basically done what they do with the modern redefinitions of the metre - the distance travelled by light in 1/299792458 ths of a second. Obviously they chose that number to keep the definition in line with the original, but they could have done that with the original definition to make the metre basically any length they wanted, but they didn’t.