When a watch meets the requirements of the ISO 3159/DIN 8319, it can be labeled as a chronometer watch. This international standard aims to evaluate the performance of the watch. The test is often performed by independent testing bodies like the COSC or the Contrôle Officiel Suisse des Chronomètres based in Switzerand. On top of that, watches undergo chronometer testing done by separate institutes. The German Glashütte Observatory in Saxony and the French observatory at Besançon are the most popular institutes that perform chronometer testing. Until now, there is no guarantee which is more effective whether to have it tested by third party certification bodies or to have it internally tested by the brand company.
Before the international standards were established, the term was widely used in the watch making industry as long as it apply to watches and clocks that are high precision and performance. It is commonly referred to marine chronometers. There was also a time that chronometer is referred to as the detent or the chronometer escapement. This term was originally used by the clockmaker in UK named Jeremy Thacker. He used it in 1714 in the attempt of making a marine chronometer design. His optimistic work failed during his time.
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