COSC

COSC is an acronym for the organization's French language name, Contrôle Officiel Suisse des Chronomètres.

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.

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).

Pre-owned and vintage chronometers generally require a complete service in order to be restored to COSC-levels of performance.

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).

200 shocks equivalent to 100 g (981 m/s², 3,217 ft/s²) A COSC certified mechanical chronometer is tested for 15 days and checked with two key pieces of data: A COSC certified quartz chronometer is tested for 13 days, in one position, at 3 different temperatures and 4 different relative humidity levels.

[citation needed] 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.

Over a million official chronometer certificates are delivered each year, representing only 3% of the Swiss watch production.

[23][24] 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.

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.

Rolex by far submits the largest number of movements to COSC, over a million a year, followed by Omega, Tudor, Breitling, Mido and Tissot.

Unlike the ISO 3159 Timekeeping instruments — Wrist-chronometers with spring balance oscillator standard, it is no longer just the uncased movements that are tested, but completely assembled watches.

[28] Finally, the movement and the watch must be subjected to 10 test cycles and satisfy to the 8 technical criteria of the METAS Requirements.

The 10 test cycles are operations to be performed on each movement and each watch and make it possible to obtain the values necessary for the calculation of the 8 criteria.

Instant running achieves this over short periods of time (30 seconds) while the daily precision is taken between 23 and 26 hours.

The highlights of this certification are in particular the test of the resistance of the watch in relation to magnetic fields and the tight limits for the average daily precision.

This being the case, the totality of the checks (magnetism, operation, and water resistance) guarantees a very high-quality mechanical watch for the end customer.

The first mechanical watches that met the METAS Certified Master Chronometer requirements featured Omega 8900 series automatic movements.