Information about Cosc

This article is about the Swiss Official Chronometer Testing Institute, known by its French language acronym of COSC. For the state college in Connecticut, see Charter Oak State College.

COSC a/k/a C.O.S.C. is the Official Swiss Chronometer Testing Institute.

Background

Founded in its current structure in 1973, the COSC ("Contrôle Officiel Suisse des Chronomètres") is the Official Swiss Chronometer Testing Institute. It is a non-profit organization. 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 onward.

Presently, three laboratories do the actual testing of the movements submitted by individual watch manufacturers to be granted the official chronometer status, located in Biel/Bienne, Geneva & Le Locle. The Geneva and Biel laboratories are almost entirely devoted to testing Rolex movements. Notwithstanding, the production of Rolex is not 100% chronometers. However, Breitling has claimed to that since the year 2000, 100% 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 see also (since 1988) (and variants 3155, 3175, 3185, 4130) and 2235, the ETA 2892A2 (and variants) and the Valjoux 7750. Each of these movements operates with an oscillation frequency of 28,800 beats per hour.

Standards and Methods

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

Testing criteria is based on ISO 3159 version 1976 which provides the definition of 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

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, the minima of which must all 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. COSC have also developed their own standard for testing quartz chronometers with eight eliminatory criteria, also note in the table below.

COSC Requirements

Mechanical	Quartz
* Average daily rate: -4/+6 [1]	* Average daily rate at 23 °C: ± 0.07
* Mean variation in rates: 2 [2]	* Rate at 8 °C: ± 0.2
* Greatest variation in rates: 5 [3]	* Rate at 38 °C: ± 0.2
* Difference between rates in H & V positions: -6/+8 [4]	* Rate stability: 0.05
* Largest variation in rates: 10 [5]	* Dynamic rate: ± 0.05
* Thermal variation: ± 0.6 [6]	* Temporary effect of mechanical shocks: ± 0.05
* Rate resumption: ± 5 [7]	* * Rate resumption: ± 0.05
* n/a	* Residual effect of mechanical shocks: ± 0.05; 200 shocks equivalent to 100 G (981 m/s²)

Measurements are based on a time base established by two independent atomic clocks synchronized on GPS time. Not all chronometers are supplied with the report issued by the COSC as the reports are optional to the brand or maker. Only the manufacturers may decide whether they want to reveal or not the results gathered during the certification process of the movement by the COSC. For example, Rolex and Omega do not supply their chronmoter certified watches with the COSC certificates. However, Omega can provide COSC chronometer certificates upon the buyer's request.

Observatory Trials and the Standards before 1973

While competitive chronometer testing took place at the Observatories in Neuchâtel (1866-1975) and Geneva (1873-1967), testing of large numbers of watches intended for public sale was conducted by the independent Bureaux officiels de contrôle de la marche des montres (B.O.’s) established between 1877 and 1956. Between 1961 and 1973, “a chronometer [was] a precision watch, which [was] regulated in several positions and at different temperatures and which had received a certificate [from the (“B.O.)”]. Collective certificates, rather than individual certificates, were usually issued. The 1961-73 standard required a mean daily rate in five positions of -1/+10. In 1973, the B.O.’s came under the C.O.S.C. which specified a daily rate of -4/+6 sec.

The value of COSC certification

Only 3% of Swiss Watch Production is COSC Certified

Over 1 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.^[8]

Meaningful Test or a Simple Marketing Gimmick?

There is a debate among watch enthusiasts as to whether the C.O.S.C. 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 C.O.S.C. testing, they frequently employ additional jewelling (i.e. to the barrel) and; better quality "assortiment" parts (i.e. higher quality hairsprings, mainsprings, balance wheels; regulators, etc.) all aimed at the coveted chronometer certification.^[9] On the other hand, many enthusiasts are of the opinion 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 C.O.S.C. Movements so submitted are more likely than not submitted with better quality parts and as a consequence may be more likely to maintain better timekeeping rates over longer periods of time.^[10]

Exemplar Brands Submitting to COSC

Among others, Baume & Mercier, Breitling, Chopard, Chronoswiss, Ebel, Girard-Perregaux, Omega, Patek Philippe, Rolex, Stowa, Ulysse Nardin, Vacheron Constantin and Zenith are brands that submit, at least some of their movements, for COSC certification. Audemars Piguet, Breguet, IWC, Jaeger-LeCoultre, A. Lange & Sohne, and Piaget are among the very top tier brands that do not submit their movements to COSC for certification.

A Proper Perspective

For a proper perspective, it is important to bear in mind that the fine regulation and chronometer characteristics of a watch can be destroyed in seconds by a rough and inexperienced hand. ^[11]

References

See also/Compare

• British Horological Institute
• Fondation Qualité Fleurier
• Geneva seal
• Master Control 1000 hours Test Versus COSC
• Inside the COSC

External links

• (Fr.) ISO 3159 (1976) Standard
• Contrôle Officiel Suisse des Chronomètres
• Federation of the Swiss Watch Industry FH
• How to read a COSC Certificate
• Can a non-certified watch meet the precision criteria of a chronometer?