A chronometer was any instrument that measures time, as a clock, watch, or dial; but, specifically, this term is applied to those time-keepers which were used for determining the longitude at sea, or for any other purpose where an accurate measure of time was required, with great portability in the instrument. The chronometer differed from the ordinary watch in the principle of its escapement, which was so constructed that the balance was free from the wheels during the greater part of its vibration, and also in being fitted with a compensation adjustment, calculated to prevent the expansion and contraction of the metal by the action of heat and cold from affecting its movements. Marine chronometers generally beat half-seconds, and were hung in gimbals in boxes 6 or 8 inches square. The pocket chronometer did not differ in appearance from a watch except that it was somewhat larger. Research Chronometer
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Research Chronometer