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COSC aka C.O.S.C. is Contrôle Officiel Suisse des Chronomètres, the Official Swiss Chronometer Testing Institute, which is the institute responsible for certifying the accuracy and precision of watches in Switzerland.
 

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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.[1] 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 [2][3] 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 COSC was founded by five watchmaking cantons (states) 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, Geneva and Le Locle. The Geneva and Biel laboratories are almost entirely devoted to testing Rolex movements.[4] Although not all Rolex watches are chronometers, Breitling has claimed that since 2000 all of its production is COSC certified. Since its inception in 2006 Bremont watch has had its entire line COSC certified as well. 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[5] are the Rolex 3135[6] (since 1988) (and variants 3155, 3175, 3185, 4130) and 2235, the ETA 2892A2[7] (and variants) and Valjoux 7750,[8] each of which operates at 28,800 beats per hour.

Each officially certified COSC chronometer is identified by a serial number engraved on its movement and a certification number given by the COSC.

Testing criteria are based on ISO 3159[9] which defines a wrist chronometer with spring-balance oscillator. Only movements which meet the precision criteria established under ISO 3159 are granted an official chronometer certificate. Compare ISO 3158.[10]

Each uncased movement is individually tested for fifteen days, in five positions, at three different temperatures. The movements are fitted with a seconds hand and the automatic winding mechanisms are disengaged for the tests. Measurements are made daily with the aid of cameras. Based on these measurements, seven eliminatory criteria are calculated, each of which must be met e.g. for movements of a diameter over 20 mm, the requirements, indicated in seconds/day, are noted in the table below. There is no ISO standard for quartz timepieces, but there is development in this field. ISO 10553:2003 specifies the procedure for evaluating the accuracy of quartz watches, individually and by lot, and the relationship between the accuracy tested and the accuracy classification given by the manufacturer. It applies to quartz watches having accompanying documents on which the accuracy classification is indicated.

Only 3% of Swiss Watch production is COSC certified

Over a million official chronometer certificates are delivered each year, representing only 3% of the Swiss watch production, a proportion that underscores the exceptional nature of a chronometer. To earn chronometer certification, a movement must not only be made from the highest quality components, but also be the object of special care on part of the finest watchmakers and timers during assembly.

Meaningful test or marketing gimmick?

There is a debate among watch enthusiasts as to whether the COSC chronometer certification for a Swiss watch is a meaningful test or a simple marketing gimmick. On the one hand, when a watch maker intends to submit a movement for COSC testing, they frequently employ additional jewelling (i.e. to the barrel) and better quality[21] "Ébauche" parts (i.e. higher quality hairsprings, mainsprings, balance wheels; regulators, etc.) all aimed at the coveted chronometer certification.[22] On the other hand, it is likely that most good quality movements on the market today are capable of being tweaked, and timed to fall comfortably within the benchmark -4/+6 average daily rate criteria of the COSC. However, movements so submitted to COSC are more likely to be submitted with better quality parts in order to be confident of a successful test, and as a consequence may be more likely to maintain better timekeeping rates over the service life of the time piece.[23]

Therefore, some of the ″Haute Horlogerie″ Swiss Watch Manufacturers have created on 5 June 2001, ″The Fleurier Quality Foundation″ to establish new aesthetic and technical criteria dedicated to the certification of finished watches. Their certification meets a normative requirement for the market and the final customer to have a better definition of quality watchmaking, adapted to today's demands and technological advances. Geneva's have created along similar criteria the Geneva seal.

From - http://en.wikipedia.org/wiki/COSC
 

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Thanks for the info.

I have read this before and it's good info to have.


What's amazing to me is that it doesn't cost that much to have the movement tested/certified (approx $45 pass or fail). For brands/models to enter another realm of perceived quality and exclusivity, a COSC certificate is worth the money (I would pay for it). Unfortunately, an issue arises when your movements are routed out-of-house to a facility for up to 3 weeks (including travel, excluding customs [not all COSC movements are encased in Switzerland]) while they are COSC certified.
 

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thank you James for the cosc information. ....bob
 
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