What Is COSC?
Little known to the general public, the COSC plays a pivotal role — and the sterling worldwide reputation of Swiss watchmaking owes no small debt to its work. Founded at the initiative of five watchmaking cantons (Geneva, Bern, Solothurn, Neuchâtel and Vaud) and the Federation of the Swiss Watch Industry, the COSC's primary mission is to measure and verify the precision of watch movements in order to award them the title of Certified Chronometer.
This designation serves as the ultimate guarantee of a high-precision timepiece, uniting irreproachable quality with unrivalled horological expertise.
What is a movement?
A watch movement, also known as a calibre, is the engine of a timepiece — the powerhouse that drives the watch and all of its functions. This intricate internal mechanism moves the hands and powers every complication, from a chronograph and annual calendar to a dual time zone display. The movement governs all timekeeping functions and is essential to the accuracy of the watch. Without it, a timepiece simply would not work.
While new movements continue to emerge, there are essentially two principal families: mechanical movements and quartz movements. An easy way to distinguish a quartz from a mechanical movement is to observe the seconds hand. On a quartz watch, the seconds hand ticks in discrete, once-per-second increments, whereas on a mechanical watch, it sweeps in a smooth, continuous motion.
How Is a Watch Awarded Certified Chronometer Status?
The COSC tests three types of mechanical instruments and one type of quartz instrument. For mechanical movements, specialists verify the regularity of rate over a 15-day testing period, analysing data related to temperature and the orientation of the watch. The movements are briefly removed from their thermal chambers for a matter of seconds in order to take measurements using machines equipped with an array of cameras. The permitted rate deviation falls between -4 and +6 seconds per day. It is always preferable for a watch to run slightly fast rather than slow.
Quartz movements are subjected to temperature and humidity testing. Once COSC-certified, each calibre is assigned a unique serial number before being returned to its manufacture of origin for casing. It is worth noting that the COSC certifies movements, not finished watches.
For more information on watch movements
Our AUBERI experts are at your disposal. For the servicing or repair of your timepiece, our watchmaking workshop offers a comprehensive maintenance service carried out by our certified master watchmaker.
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