Ligne
Modern equivalent
Watchmaking: 2.2558 mm. Buttons: 0.635 mm (1/40 inch)
A fine measure of diameter surviving in two distinct trades, at two quite different sizes.
The watchmaker’s ligne descends from the old French inch divided into twelve, and movement diameters are still quoted in it: a calibre described as 11.5 lignes measures about 25.9 millimetres. The button ligne is a different unit entirely, fixed at one fortieth of an inch, so that a 40-ligne button is one inch across. The two share a name, an origin in fine trade measurement and nothing else, differing by a factor of three and a half. Anyone meeting the word without knowing which trade is meant will be wrong by a considerable margin.