My Luxury Watch is COSC Certified Chronometer. What does that mean?

What does the abbreviation COSC represent? The Contrôle Officiel Suisse des Chronomètres - The Official Swiss Control Office for Chronometers.

Who is the COSC? C.O.S.C. was founded ,as it is currently known, in 1973. It is a Swiss non-profit organization that tests Swiss-made chronometers.
Who founded COSC? COSC was founded by five watchmaking regions of Switzerland: Bern, Geneva, Neuchatel, Solothurn and Vaud, in conjunction with the Federation of the Swiss Watch Industry (FHS). It includes the laboratories/ observatories that were created independantly of each other from the late 1800's.

What is the role of COSC? COSC tests the movements of timepieces submitted by individual watch manufacturers to be granted the status of chronometer.

Where is COSC located? COSC have testing laboratories in three different locations: Biel/Bienne, Geneva and Le Locle. The Laboratories in Geneva and Biel are almost completely dedicated to testing Rolex movements.

Which movements calibres obtain most of the COSC certificates? The Rolex 3135 (since 1988) variations of which are 3155,3175,3185,4130; Rolex 2235; the ETA 2892A2, and its variants; Valjoux 7750. Each of these movements operate at 28,800 beats per hour.

Bretling claims that all its watches that have been manufactured since 2000 are COSC certified, Rolex and Omega watches have a large selection of their watches which are COSC certified.

How can you tell if a watch is COSC certified ? A Certified Chronometer has a serial number engraved on its movement and a certification number provided by the COSC.

What are the testing criteria for a chronometer? Testing criteria are based on ISO 3159 which defines a wrist chronometer with spring-balance oscillator. Only movements that meet the precision criteria are provided with an official chronometer certificate.

How is the watch tested? Actually only the uncased movements are tested, not the entire watch. The movements are individually tested for 15 days, in 5 different positions at 3 different temperatures. The movements are fitted with a seconds hand. The automatic winding movement is disengaged for the test. Daily measurements are made with the assistance of a camera. Once these measurements have been obtained, 7 criteria are calculated, each of which must meet the syandards of the COSC.

I know that these criteria are solely for mechanical watches. What about quartz watches? Currently there are no ISO standards for quartz timepieces, but COSC has developed its own standard for testing quartz chronometer with eight eliminatory criteria.

How difficult is it for a watch to become an Official COSC Certified Chronometer? Well judging from the fact that only 3% of the entire swiss watch production is COSC Certified, exceptionally difficult. This percentage only accentuates the fact of the outstanding nature of the chronometer. Inorder to receive the chronometer certificate, a movement must be crafted from the highest quality components, and be crafted with special care, by the finest watchmakers and timers during assembly.

Which brands submit their movements to the COSC? Baume & Mercier, Breitling, Chopard, Ebel, Girard-Perregaux, Omega, Patek Phillipe, Rolex, Tag Heuer, Ulysse Nardin, Vacheron Constantin and Zenith.

Which brands do not submit their movement to the COSC? Audemars Piguet, Breguet, IWC, Jaeger-LeCoultre, A. Lange & Sohne and Piaget.

My Watch has a Chronograph, does that mean it is a Chronometer? NO! Chronograph and Chronometer are two completely different terms used in association with a timepiece.

A "Chronograph" is a timepiece that is fitted with an additional mechanism that may be set in motion by knobs to enable the measurement of the duration of an event.

A "chronometer" is a high-precision watch capable of displaying the seconds and housing a movement that has been tested over several days, in different positions and at different temperatures, by an official neutral body (COSC).
Each movement is individually measured. Any watch with the denomination "chronometer" is provided with a certified movement.

The Contrôle Officiel Suisse des Chronomètres or COSC (The Official Swiss Control Office for Chronometers) reported record figures for 2007. The number of certificates registered in 2007 was up 13.3 per cent from 2006 making that a total number of 1,538,676 registrations.

The top three companies applying for registration were Rolex with 728,255 certificates, Omega with 341,161 and Breitling with 222,650.

The perfect accuracy of a chronometer can be destroyed with rough handling and little maintenance.

There is an ongoing debate, by watch enthusiasts whether the COSC Certification is a significant test or simply a marketing gimmick? A watch maker proposing to submit a movement for COSC testing, add additional jeweling (i.e. to the barrel) and superior quality "assortment" parts such as greater quality hairspring, mainsprings, balance wheels, regulators and so on. The aim is to obtain the highly regarded COSC Chronometer Certification. On the other hand, some watch enthusiasts believe that with today's innovations used in watch making, most high-end, good quality movements are capable of being adjusted and timed in order that they will fall between the COSC criteria of -4/+6 average daily rate. Movements that are presented are more likely than not, presented with better quality parts, and as a result may be less likely to maintain better timekeeping rates over longer periods.