A binnacle is a waist-high case or stand on the deck of a ship, generally mounted in front of the helmsman, in which navigational instruments are placed for easy and quick reference as well as to protect the delicate instruments. Its traditional purpose was to hold the ship's magnetic compass, mounted in gimbals to keep it level while the ship pitched and rolled. A binnacle may be subdivided into sections and its contents typically include one or more compasses and an oil lamp or other light source. Other devices such as a sand timer for estimating speed may have been stored in the binnacle as well.

With the introduction of iron-clad ships the magnetic deviation observed in compasses became more severe. Methods of compensation by arranging iron or magnetic objects near the binnacle were developed. In 1854, a new type of binnacle was patented by John Gray of Liverpool which directly incorporated adjustable correcting magnets on screws or rack and pinions. This was improved again when Lord Kelvin patented in the 1880s another system of compass and which incorporated two compensating spheres. These are colloquially known as "Kelvin's balls" in the UK, and "navigator's balls" in the United States. Unlike most display binnacles today, which have the balls painted red and green to represent port and starboard side of the vessel, the balls were painted black or some other uniform color. The Royal Maritime museum at Greenwich, London, has an extensive collection of binnacles.

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