[applfanboysbgon]

You had the right idea. Angstroms are not an SI unit. The SI units jump by three orders of magnitude at this scale: picometer, nanometer, micrometer, millimeter.

(In the same way that meter jumps three orders of magnitude to kilometer[1], or millions to billions to trillions, etc.)

[1] Technically there are intermediate SI units between meter and km but nobody uses them. There are not intermediate SI units between the tiny ones.

[SoftTalker]

Why above 1mm do we go by tens instead of thousands?

We have centimeter (10 mm) then decimeter (100mm) then meter (1000mm). Then we jump to thousand again (kilometer).

[floxy]

>We have centimeter (10 mm) then decimeter (100mm)

Does anyone actually use those? I think I would throw up a little in my mouth if I saw either of those on a mechanical drawing.

[bonzini]

Decimeter is used occasionally for densities, because 1 g/cm^3 is the same as 1 kg/dm^3 but the latter is a little easier to imagine. The cube decimeter is also used under the name of... liter.

Likewise, there is also deca- and hecto-. Hectograms are used for shopping.

Decameter (dam, 10 m) is never used, but there is a non-SI unit of area based on it, called the are. Nobody uses the are, but its multiple the hectare (1 square hectometer) is common in some countries when talking about land plots. It's a little less than 2.5 acres, for people in the US.

[mikko856]

Centimeter is the commonly used metric for small distances in everyday parlance, just like an inch.

[topspin]

Answer that question and you'll get the whole impetus for logarithmic scales.

[applfanboysbgon]

Everyday necessity. The gap between mm and m is too large, there are many things in daily life that are better expressed in cm. SI units must strike a balance between three factors: not having so many denominations nobody can remember them; not having so few denominations that using them adds too much wordiness to daily life (150mm or 0.15m are wordier than 15cm); and a degree of familiarity with the everyday units people used before metric, to smooth the transition and encourage adoption.