Marine chronometer
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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
A marine chronometer by Charles Frodsham of London, shown turned upside down to reveal the movement. Chronometer circa 1844–1860.
The marine "Chronometer" of Jeremy Thacker used gimbals and a vacuum in a bell jar.
Henry Sully (1680–1729) presented a first marine chronometer in 1716
John Harrison's H1 marine chronometer of 1735
Longitude
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Longitude is a geographic coordinate that specifies the east-west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees
The clockwork in John Harrison's H4 marine chronometer on display at the Royal Observatory, Greenwich
Marine sandglass MMM