210. watch-knowledge


A visit to the COSC, the temple of Swiss chronometry testing

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October 2011



We often see the mention “COSC certified” associated with a watch, although, in reality, it applies to only three per cent of Swiss timepieces. With its abbreviation standing for “Contrôle Officiel Suisse des Chronomètres,” what exactly is the COSC? What exactly does it certify? And how exactly does the COSC arrive at these certifications? To learn more, Europa Star travelled to the Bienne office of the COSC (the other two offices are located in La-Chaux-de-Fonds and Geneva).

At the risk of overstating the obvious to the majority of our professional readers, we must remind everyone that a “chronometer” is not a “chronograph”. According to the COSC’s own definition, “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). Only movements which meet the precision criteria established under ISO 3159 are granted an official chronometer certificate.”
Although the definition sums it up, it is still necessary to explain things a bit more. Let’s start with the famous “ISO Standard 3159” that the managers of COSC call—respectfully but with a slight smile—“the Bible” of the chronometer. Among the other specifications decreed by this standard (which is subject to copyrights and therefore cannot be reproduced here in detail), the primary principles are based on certain qualifying criteria that have to be met in order to achieve the certification. The table sums them up.

A visit to the COSC, the temple of Swiss chronometry testing

Statistical precisions
In 2010, exactly 1,276,714 movements were certified by the COSC. These were primarily mechanical movements although quartz certification does exist, even if it is not very common (only 19,799 quartz movements were certified in 2010). The COSC, an independent and official organisation, is legally a not-for-profit association, created in 1973 by five watchmaking cantons (Bern, Geneva, Neuchâtel, Solothurn, and Vaud) as well as by the Federation of the Swiss Watch Industry (FH ).
The COSC publishes the certifications obtained for each brand, thus incidentally communicating information that would normally be confidential to certain companies. Three large brands make up the lion’s share of COSC certifications: Rolex with 611,424 certified chronometers in 2010, followed by Omega with 342,798 certificates, and then Breitling with 122,649 certificates. Among the remainder of the certificates obtained in 2010, in decreasing order, are: Chopard with 34,254; Panerai with 26,291; Mido with 25,384; TAG Heuer with 24,541; and Titoni with 13,335.
The overall failure rate, year in and year out, is approximately five per cent for the pieces that undergo these tests.

A visit to the COSC, the temple of Swiss chronometry testing

A 16-day testing cycle
The certification cycle lasts sixteen days. All the movements to be tested are given a unique identification number engraved on the movement and a generic dial used for the tests, whose standards are specified by the COSC. This dial comprises a system of reference points that permits the absolute centring of the image and renders the measurement insensitive to the tolerance of the position of the movement when it is placed under the camera.
Each watch comes to the COSC with all its technical specifications detailed by the brand (for example, movements with additional plates are tested with them mounted). A barcode is attributed to each piece to allow for total traceability. The first operation is the identification of the pieces in the COSC’s computer system, then their packaging in the trays before being automatically wound, followed by a rest period of 24 hours before undergoing their first measurement.
For the next fifteen days, including Saturdays and Sundays, a series of repetitive tests is performed. In the first step, the time indicated by the watch is individually recorded on a server controlled by an atomic clock. This recorded reference time will allow the determination of the successive tolerances in the movement’s operation. Between the tests, the movement will be placed in five different positions (vertical at 6 o’clock, at 3 o’clock, and at 9 o’clock, and horizontal, on the dial side and then on the movement side) and at the three different temperatures of 23°C, 8°C and 38°C.

A visit to the COSC, the temple of Swiss chronometry testing

The daily measurement determines the state of the movement’s operation (in other words, the time displayed by the movement) in relation to the reference time. This measuring by “differentiation of states” makes it possible to integrate the behaviour of the movement over time, as the COSC says, since it takes into account the variations in amplitude as well as small mechanical perturbations inherent in each movement.
The tests are conducted using industrial vision systems: a CCD cell is coupled with an optical sensor that detects the position of the seconds hand on the dial division. Data recording and calculation are all automated.
The same procedures, but conducted manually, are reserved for movements with special features—for example, particular escapements—or unique pieces that require an individual protocol (this system will be used for the finished watches that are entered in the next Chronometry Competition). And, as calibres have grown in size over the last decade, the machines employed by the COSC have had to be adapted to the new dimensions.
So, what does it cost the brands to have their watches certified as “chronometers”? For large series pieces, the cost is CHF 5.25 per piece, while for special cases using manually controlled testing, the price is CHF 130. (This testing amounts to the tidy sum of more than CHF 3 million for Rolex, for example, without counting its administrative costs).

A visit to the COSC, the temple of Swiss chronometry testing

The value of a certificate
Is all this worth it? Definitely, yes. Having a COSC certificate brings additional prestige to a watch, especially when only three per cent of Swiss watches are COSC certified. Yet, the system is not without its detractors and among the criticisms are that the movements are tested before being placed in their cases, which can also have a negative influence on a piece’s operation, and that self-winding movements are tested without their oscillating weight.
Bernard Dubois, director of the COSC in Bienne, says that he understands these criticisms. But to test such a large number of encased watches per year would require a complete overhaul of the equipment and the procedures because the watches all have very different specifications (and how can the tests precisely measure the operation using dials of all colours, whose degrees of readability are quite different?).
The COSC certification thus remains a very valid credential, even if conditions may be somewhat altered by an ill-fated encasing. In this case, the ball is in the court of the brands that must remain vigilant as to the quality of their casing and test them severely. This is extremely important since how many clients will accept that their COSC-certified watch advances or retards by a higher delta than the one officially claimed? It is also important not only for the credibility of the COSC but also for the Swiss watch community for which the COSC remains a strong marketing tool—and we all know the importance of marketing.

Source: Europa Star October - November 2011 Magazine Issue