chronometer
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Harrison's No.4 chronomeer
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An extremely accurate clock, especially one used in connection with celestial navigation at sea (see also celestial sphere). It differs from an ordinary clock in that it has a fusee, by means of which the power transmission of the mainspring is regulated such that it remains approximately uniform at all times; and a balance made of metals of different coefficients of expansion to minimize the effects of temperature changes. The device is maintained in gimbals to reduce the effects of rolling and pitching. A chronometer's accuracy is checked daily and its error noted; the daily change in error is termed the daily rate.
Chronometers are always set to Universal Time (Greenwich Mean Time). The first chronometer was invented by John Harrison (1735).
Related categories
• INSTRUMENTATION
• TIME MEASUREMENT AND PUZZLES
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