COSC

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.

Founded in its current form in 1973, the COSC is a Swiss non-profit organization that tests Swiss-made chronometers. COSC is an acronym for the organization's French name, Contrôle Officiel Suisse des Chronomètres.

COSC testing generally applies to watches manufactured/assembled in Switzerland. Notwithstanding, the normative standards are set by international agreement and are the same whether they are nominally labeled ISO or DIN standards. Some German, Japanese, and even non-certified Swiss movements can surpass the normative requirements. The Japanese have largely abandoned the accolade, replacing it with in-house testing to a slightly more strict standard as with, for example, the Grand Seiko. On the other hand, the Germans have set up their own testing facility in Saxony at the Glashütte Observatory where the DIN 8319 standards, which mirror the ISO standards used by COSC, are employed. At one time the French provided similar large scale testing at the Observatory at Besançon, however, today only a very few watches are currently tested there and carry the accolade "Observatory Chronometer."

The organization 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.

Three laboratories now test the movements submitted by individual watch manufacturers to be granted chronometer status. They are in Biel/Bienne, Saint-Imier/BE and Le Locle. The Saint-Imier and Biel laboratories are almost entirely devoted to testing Rolex movements. Although not all Rolex watches are chronometers, Breitling has claimed that since 2000 all of its production is COSC certified. Omega also has much of its production certified. Thus, based upon the movements used by Rolex, Breitling, and Omega, the movement calibers that obtain most of the COSC certificates are the Rolex 3135 (since 1988) (and variants 3155, 3175, 3185, 4130) and 2235, the ETA 2892A2 (and variants) and Valjoux 7750, each of which operates at 28,800 beats per hour. Tag Heuer and Ball watches both have select watches designated as chronometers which are sent to COSC for certification.

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