Apparently Aristotle was impressed by the improvisation of the craftsmen that he was watching on the island of Lesbos. They were building rounded columns for which rigid rulers were useless. The craftsmen improvised with a ruler that bends – which we call a tape measure...

And this is the nature of the equitable, a correction of law where it is defective owing to its universality. ... For when the thing is indefinite the rule also is indefinite, like the leaden rule used in making the Lesbian moulding; the rule adapts itself to the shape of the stone and is not rigid, and so too the decree is adapted to the facts. 

Aristotle. "Nicomachean Ethics" quoted by David Herbert in Rigid Rules