A chronometer (χρονόμετρον, khronómetron, "time measurer") is an extraordinarily accurate mechanical timepiece, with an original focus on the needs of maritime navigation. In Switzerland, timepieces certified by the Contrôle Officiel Suisse des Chronomètres (COSC) may be marked as Certified Chronometer or Officially Certified Chronometer. Outside Switzerland, equivalent bodies, such as the Japan Chronometer Inspection Institute, have in the past certified timepieces to similar standards, although use of the term has not always been strictly controlled.
The term chronometer was coined by Jeremy Thacker of Beverley, England in 1714, referring to his invention of a clock ensconced 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 that enabled accurate marine navigation. From then on, an accurate chronometer was essential to open-ocean marine or air navigation out of sight of land. Early in the 20th century the advent of radiotelegraphy time signals supplemented the onboard marine chronometer for marine and air navigation, and various radio navigation systems were invented, developed, and implemented during and following the Second World War (e.g., Gee, Sonne (a.k.a. Consol), LORAN(-A and -C), Decca Navigator System and Omega Navigation System) that significantly reduced the need for positioning using an onboard marine chronometer. These culminated in the development and implementation of global satellite navigation systems (GSN-GPS) in the latter half of the 20th century. The marine chronometer is no longer used as the primary means for navigation at sea, although it is still required as a backup, since radio systems and their associated electronics can fail for a variety of reasons.
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.
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Quartz clocks and quartz watches are timepieces that use an electronic oscillator regulated by a quartz crystal to keep time. This crystal oscillator creates a signal with very precise frequency, so that quartz clocks and watches are at least an order of magnitude more accurate than mechanical clocks. Generally, some form of digital logic counts the cycles of this signal and provides a numerical time display, usually in units of hours, minutes, and seconds.
A watchmaker is an artisan who makes and repairs watches. Since a majority of watches are now factory-made, most modern watchmakers only repair watches. However, originally they were master craftsmen who built watches, including all their parts, by hand. Modern watchmakers, when required to repair older watches, for which replacement parts may not be available, must have fabrication skills, and can typically manufacture replacements for many of the parts found in a watch.
Rolex SA (ˈroʊlɛks) is a Swiss watch designer and manufacturer based in Geneva, Switzerland. Founded in 1905 as Wilsdorf and Davis by Hans Wilsdorf and Alfred Davis in London, the company registered Rolex as the brand name of its watches in 1908 and became Rolex Watch Co. Ltd. in 1915. After World War I, the company moved its base of operations to Geneva because of the unfavorable economy in the United Kingdom. In 1920, Hans Wilsdorf registered Montres Rolex SA in Geneva as the new company name (montre is French for clock or watch); it later became Rolex SA.
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