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Harrison solved the precision problems with his much smaller H4 chronometer design in 1761.

H4 looked much like a large five-inch (12 cm) diameter pocket watch.

To determine a position on the Earth's surface, it is necessary and sufficient to know the latitude, longitude, and altitude.

Altitude considerations can naturally be ignored for vessels operating at sea level.

Attempts to construct a working marine chronometer were begun by Jeremy Thacker in England in 1714, and by Henry Sully in France two years later.

Sully published his work in 1726 with Une Horloge inventée et executée par M.

This was followed by a further theoretical description of a chronometer in works published by English scientist William Derham in 1713.

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The first published use of the term was in 1684 in Arcanum Navarchicum, a theoretical work by Kiel professor Matthias Wasmuth.The lunar distances method, initially proposed by Johannes Werner in 1514, was developed in parallel with the marine chronometer.The Dutch scientist Gemma Frisius was the first to propose the use of a chronometer to determine longitude in 1530.The first true chronometer was the life work of one man, John Harrison, spanning 31 years of persistent experimentation and testing that revolutionized naval (and later aerial) navigation and enabling the Age of Discovery and Colonialism to accelerate.The term chronometer was coined from the Greek words chronos (meaning time) and meter (meaning counter) in 1714 by Jeremy Thacker, an early competitor for the prize set by the Longitude Act in the same year.Sulli, but neither his nor Thacker's models were able to resist the rolling of the seas and keep precise time while in shipboard conditions.

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