COSC
The Contrôle Officiel Suisse des Chronomètres, the Official Swiss Chronometer Testing Institute, is the institute responsible for certifying the accuracy and precision of Swiss watches.
Background
Founded in its current form in 1973, the COSC is a Swiss non-profit organization that tests chronometers that are Swiss Made. COSC is an acronym for the organization's French language name, Contrôle Officiel Suisse des Chronomètres.COSC testing generally applies to watches manufactured or 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. It encompasses the laboratories and 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 and 2235, the ETA 2892A2 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.
Standards and methods
Each officially COSC certified 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 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.
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. 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. Nevertheless, COSC has also developed its own standard for testing quartz chronometers with eight eliminatory criteria, also noted in the table below.
| Mechanical | Quartz |
| Average daily rate: −4/+6 | Average daily rate at 23 °C: ±0.07 |
| Mean variation in rates: 2 | Rate at 8 °C: ±0.20 |
| Greatest variation in rates: 5 | Rate at 38 °C: ±0.20 |
| Difference between rates in H & V positions: −6/+8 | Rate stability: 0.05 |
| Largest variation in rates: 10 | Dynamic rate: ±0.05 |
| Thermal variation: ±0.60 | Temporary effect of mechanical shocks: ±0.05 |
| Rate resumption: ±5 | Rate resumption: ±0.05 |
| n/a | Residual effect of mechanical shocks: ±0.05; 200 shocks equivalent to 100 g |
| n/a | Humidity: ±0.10 |
A COSC certified mechanical chronometer is tested for 15 days and checked with two key pieces of data:
- temperature
- the position of the movement
Measurements are compared with 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. Each manufacturer may decide whether to reveal the results gathered during the certification process of the movement. For example, Breitling do supply all their watches with COSC certificates however Rolex and Omega do not supply even their chronometer certified watches with the COSC certificates. Omega however can provide the COSC chronometer certificate if asked.
Observatory trials and standards before 1973
While competitive chronometer testing took place at the observatories in Neuchâtel and Geneva, testing of large numbers of watches intended for public sale was conducted by the independent Bureaux officiels de contrôle de la marche des montres established between 1877 and 1956. Between 1961 and 1973, “a chronometer a precision watch, which regulated in several positions and at different temperatures and which had received a certificate ." 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 are COSC certified
Over a million official chronometer certificates are delivered each year, representing only 3% of the Swiss watch production. 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 and better quality "Ébauche" parts all aimed at the coveted chronometer certification. 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.Therefore, some of the ″Haute Horlogerie″ Swiss Watch Manufacturers have created on 5 June 2001, 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.
Exemplar brands submitting to COSC
by far submits the largest number of movements to COSC followed by Omega, Breitling, TAG Heuer and Panerai.Rolex and Breitling submit all movements for certification, but other manufacturers only submit certain models.
Certification in perspective
Fine regulation and chronometer characteristics of a watch can be destroyed in seconds by a rough and inexperienced hand.Considering the fact that mechanical watches are almost never used for real timekeeping and navigation anymore, certification may be considered a historic relic by some, but it verifies the accuracy and quality of a mechanical movement.