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COSC is Contrôle Officiel Suisse des Chronomètres, the Official Swiss Chronometer Testing Institute, which is the institute responsible for certifying the accuracy and precision of wristwatches in Switzerland.
The COSC was founded by five watchmaking cantons of Switzerland: Bern, Geneva, Neuchâtel, Solothurn and Vaud, together with the Federation of the Swiss Watch Industry (FHS). It encompasses the laboratories/observatories that had been created independently of each other from the late 19th century.
It is a non-profit organization and tends to certify Swiss-made movements. There are today 3 main laboratories in Switzerland: Biel, Le Locle and Saint-Imier. The first one is almost dedicated to Rolex watches based on the amount of annual certification requests. Despite the fact that not all Rolex movements are chronometers, every single movement get a COSC certification. Some brands also tend to certify all movements. Breitling declared that all movements are COSC certified and Omega also test ruffly all movements as well.

Certification in other countries

Other brands living in other countries like Japan decided to have their own tests. Seiko for example produces in-house a very strict and complete test for its Grand Seiko. Germany has also developed its own center for testing based on the fact they have a strong tradition in watch-making locally. The center is located in Saxony – The Glashütte Observatory.
France has also a renowned certification institute, called the Besançon Observatory. Inspired by the Neuchâtel and Geneva observatories, the Besançon observatory tested and measured Swiss timepieces movements since
1883. A “bulletin de marche” was delivered and the mention “Observatory chronograph” could be applied.
Observatoire de Besançon

The role of the observatories during the years pushed watch-making towards a stronger accuracy of its movements.

COSC, its mission

The COSC has different missions as stated here. The first one is to measure and control the precision of watch movements in order to officially certify them as “chronometers”. To promote and defend the mention “chronometer” in the world by any mean possible. Every office is equipped with the best and the most accurate machines under the supervision of highly-skilled professionals, mostly engineers. The COSC does not manufacture any watch movements, it simply brings an extra added-value to the great work that watch-makers are already doing.
Cosc tests
Only the best high-qualitative movements can pretend to pass the test as they are very strict, testing the movement in different conditions. So when a brand wishes to develop a chronometer, we know that precision of time is crucial. So the COSC challenges watch-makers to improve themselves every year.

The COSC, the figures

Here are the certification figures published by the COSC in 2012 that reflects all thr work done by watch-makers. You can easily guess the total amount of watches produced by certain brands as some of them like Rolex and Breitling have all their movements individually certified.
Cosc annual certifications
Is it a problem if your watch does dot have a COSC certification? No. It is not an obligation. Every brand is free to request it. Only professionals can request a watch certification. Private users are not allowed to do it.
If your watch would go on heavy maintenance, that would require components replacement, the owner can request to the watch brand to have its watch retested. Of course this is feasible if the watch was already certified by the COSC.
To learn more about the COSC, please visit the official website:


When it comes to watch-making, precision is a very serious matter and the COSC is above all the ultimate reference and defender.


Info sourced at COSC website, wikipedia, La Côte des montres. All content is copyrighted with no reproduction rights available.