Marine chronometer numbered 4608, by Joseph Sewill. A two-day full-plate fusee movement. Four pillars, all fixed with blued steel screws. Punch-marked 5335. The fusee, with stop-work and Harrison's maintaining power, has a pipe round the winding square. Earnshaw-type spring-detent escapement. Compensation balance with helical balance spring.

Mounted in three-tier box, push-catch for lid and lock for upper half. Upper half has a strut limiting opening to 90 degrees. On the front of the upper half is screwed an ivory round tablet inscribed ''Ferreira' Lisboa 1895'. The box fittings are standard, with flush handles on the sides, brass gimbals and a ratchet winding key. The push-catch and lock are surrounded by shaped brass inserts. The top of the lid has a shield-shaped plain brass insert. Inside the upper half are pasted two paper labels. The first is handwritten: 'Cleaned May 1903 H. G. Blair Cardiff' and the second is a trade label for A. Johannsen & Co. On the front of the lower half is the remains of a further pasted paper label for J Garraio & C.

Silvered brass dial with Roman numerals and a large seconds dial having Arabic ten-second figures. The dial is inscribed in the centre 'J. Sewill, 30, Cornhill, Royal Exchange, London. Maker to the Admiralty'; in the seconds dial, '4608'; to left of the up-and-down dial, 'Prize medals awarded London 1862'; to right of the up-and-down dial, 'International Exhibition Paris 1867'. The up-and-down dial, below XII, is marked in Arabic numerals in 8-hour intervals up to 56 and is marked 'UP' above 0 and 'DOWN' above 56. The chronometer is in fair condition.

This chronometer was used on the famous tea clipper, Cutty Sark, when she was owned by the Portuguese under the name Ferreira.
Launched in 1869, Cutty Sark competed in the races from China to London to bring back the first of the season's tea each year. Later, in the wool trade, she repeatedly made the fastest passage home from Australia. In 1954, she was placed into a specially constructed dry-dock in Greenwich and opened to visitors in 1957.