I found this antique Chinese ruler in Seoul, ROK, last week. It uses the old Chinese units of length measure, the fēn, cùn and chǐ units.
The tiny fēn is about 3 mm. The cùn is traditionally the width of a person's thumb at the knuckle. The chǐ (or Chinese 'foot') is derived from the length of a human forearm, like a cubit. Or so says Wikipedia.
Those were hard-working people, to have thumbs as wide as a cùn.
The ruler is wooden, with brass inlays marking the units.