Marine chronometer by John Arnold, London, c.1771. Octagonal mahogany box with a glazed base and glazed windows to the case sides, probably added in the 19th century. Silvered dial, now worn to brass, with subsidiary seconds, and signed on the dial 'John Arnold London No 1'. Two small ivory handles either side of the dial enable the movement to be lifted from the case. Fusee movement with spring detent escapement, two-arm compensation balance and sun and planet maintaining power. One-day duration. Purchased by the Worshipful Company of Clockmakers for its museum in 1885.

Similar to the chronometer held by Arnold, in his family portrait by Robert Davy (Science Museum object number: 1868-248). This is one of a small group of his products signed ‘John Arnold No 1’. Arnold probably upgraded the movement more than once, fitting it with a spring detent escapement and two-arm compensation balance.