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A chronometer watch is a watch tested and certified to meet certain precision standards. In Switzerland, only timepieces certified by the COSC may use the word 'Chronometer' on them.
The term chronometer is also used to describe a timepiece used for celestial navigation.
[edit] Mechanical chronometers
Chronometers often included other innovations to increase their efficiency and precision. Hard stones such as diamond, ruby, and sapphire were often used as jewel bearings to decrease friction and wear of the pivots and escapement. Chronometer makers also took advantage of the physical properties of rare metals such as gold, platinum, and palladium.
[edit] Complications
In horology terms, a complication in a mechanical watch is a special feature that causes the design of the watch movement to become more complicated. Examples of complications include:
Quartz clocks, radio clocks, radio controlled watches, and atomic clocks have made mechanical clock-chronometers obsolete for time standards used scientifically and/or industrially, although some custom watchmakers still produce them.
[edit] Officially Certified Chronometers
Over 1,000,000 Officially Certified Chronometer certificates, mostly for mechanical wrist-chronometers (wristwatches) with sprung balance oscillators, are being delivered each year, after passing the COSC's most extreme tests and being singly identified by an officially recorded individual serial number. According to COSC, a chronometer is a high precision watch capable of displaying the seconds and housing a movement that has been tested over several days, in different positions, and at different temperatures, by an official, neutral body (COSC). Each movement is individually tested for several consecutive days, in five positions and at three temperatures. Each movement is individually measured. Any watch with the denomination "chronometer" contains a certified movement.
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