A marine chronometer is a precision timepiece that is carried on a ship and employed in the determination of the ship's position by celestial navigation. It is used to determine longitude by comparing Greenwich Mean Time and the time at the current location found from observations of celestial bodies.
This is a 2 day fusee movement marine chronometer by the makers  A. JOHANNSEN & CO as shown on the plaque to the front which reads 'A JOHANNSEN & CO. TWO DAYS. 4665' (with a military broad arrow) with a double lid for protection. Asmus Johannsen was Danish and his work was frequently submitted to the Greenwich trials where it was awarded high marks. The movement is mounted in a three-tier brass-bound mahogany box with a push-catch for lid and lock for the upper half. A silvered-brass dial has Roman numerals and a large seconds dial has Arabic ten-second figures with straight batons at alternate five-second intervals. In the seconds dial is the number 4465 and the broad arrow. The dial reads 'A Johannsen & Co. MAKERS TO THE ADMIRALTY, THE INDIAN GOVT & ROYAL NAVIES OF Italy, Spain & Portugal. 149 Minories London.  The up-and-down dial, below XII, is marked with Arabic numerals in eight-hour intervals up to 56 and is marked 'UP' above zero and 'DOWN' above 56.
Comes with photocopied paperwork of its purchase and history onboard various ships from 1898 - 1968.
Box measures 18.5cm x 18.5cm x 19cm.