Before the invention of the atomic clock, nautical clocks were what seamen relied upon for navigation purposes. Accurate clocks were needed to measure longitude. Clocks that can do this are also called maritime chronometers. They are mostly twenty-four hour analog clocks (analog clocks are those that have an hour and a minute hand.
Forerunners of the Nautical Clock
The Arabian astrolabe was another forerunner of the twenty-four hour clock. The Arabs began to add gears to their clocks in the eighth century, and these were the first mechanical clocks. The astrolabe was a model of the solar system so it counted twenty-four hours rather than twelve.
A maritime clock would indicate periods of high tide and low tide as well as positions of the moon and stars. Sometimes a barometer was included in the face along with a thermometer, as temperature and atmospheric pressure are important to seamen. Sometimes, the barometer would not be part of the same unit, but would be offered as a twin piece with the maritime clock, having an identical case. Maritime clocks were nearly always made of brass for better durability, and are nowadays valued as part of a "nautical look" decorating scheme.
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