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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 was coined by Jeremy Thacker of Beverly, England in 1714, referring to his invention of a clock ensconsed in a vacuum chamber. The term chronometer is also used to describe a marine chronometer used for celestial navigation and determination of longitude. The marine chronometer was invented by John Harrison in 1730. This was the first of a series of chronometers which enabled accurate marine navigation. For the next 250 years, an accurate chronometer was essential to any kind of marine or air navigation until the implementation of global satellite navigation at the end of the 20th century. The marine chronometer is no longer used for navigation.

Once mechanical timepiece movements developed sufficient precision to allow for accurate marine navigation, there eventually developed what became known as "chronometer competitions" at astronomical observatories located in Europe. The Neuchatel Observatory, Geneva Observatory, Besancon Observatory, and Kew Observatory are prominent examples of observatories that certified the accuracy of mechanical timepieces. The observatory testing regime typically lasted for 30 to 50 days and contained accuracy standards that were far more stringent and difficult than modern standards such as those set by COSC. When a movement passed the Observatory, it became certified as an Observatory Chronometer and received a Bulletin de Marche from the Observatory, stipulating the performance of the movement. Because only very few movements were ever given the attention and manufacturing level necessary to pass the Observatory standards, there are very few Observatory Chronometers in existence. Most Observatory Chronometers had movements so specialized to accuracy that they could never withstand being used as wristwatches in normal usage. They were useful only for accuracy competitions, and so never were sold to the public for usage. However,in 1966 and 1967, Girard Perregaux manufactured approximately 670 wristwatches with the Calibre 32A movement, which became Observatory Chronometers certified by the Neuchatel Observatory. These Observatory Chronometers were then sold to the public for normal usage as wristwatches, and some examples of this watch may still be found today. The Observatory competitions ended with the advent of the quartz watch movement, in the late 1960's and early 1970's.


Mechanical chronometers

A mechanical chronometer is a spring-driven escapement timekeeper, like a watch, but its parts are more massively built. Changes in the tension of the spring caused by variations in temperature are compensated for by devices built into it.(The Columbia Encyclopedia, Sixth Edition, 2008, Columbia University Press).

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.



In horological 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:


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.

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.

A chronometer must not lose more than four nor gain more than six seconds per day.

See also

External links


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