Geography. Usually with the. A method of ascertaining longitude at sea (also in plural). Also: a longitude clock. Obsolete.

a small chronometer formerly used in ascertaining longitude.

An instrument for measuring time; spec. applied to time-keepers adjusted to keep accurate time in all variations of temperature. They differ from…

(a) a chronometer; (b) (see quot. 1769).

A chronometer as used on board ship.

a marine chronometer mounted in a box with gimbals (cf. gimbal, n. 4).

an instrument for measuring very small periods of time.