The Contrôle Officiel Suisse des Chronomètres (COSC) functions as a sort of litmus test for precision throughout the Swiss watch industry. While the certification doesn’t necessarily have the same “wow” factor it once did, it remains a valuable aspect of how the Swiss watch industry conducts its business and, due to the intense trial each movement goes through, it’s a tried-and-true way of demonstrating the quality that Swiss mechanical watches are known for.

COSC certification is given only to Swiss Made watches

It’s another thing that there are more stringent certification processes out there. For example, a Grand Seiko certification requires watches to be the daily rate to be +5 to -3 seconds per day as opposed to the +6 to -4 for COSC certification. Here are five things that you need to know about all things COSC.  

1. Only “Swiss Made” watches can be submitted for the exam. The Swiss movement has to be assembled and tested in Switzerland, at least 60 percent of production costs are generated in Switzerland, and the value of 50 percent of the components have to be Swiss made. The main reason for the exclusion of other countries is that since the COSC functions as a non-profit, this helps ensure both the prestige and caliber of both the certification and the Swiss watch industry as a whole.

The Chronometer certificate is still a litmus test of precision

2 To have a watch pass the certification, the movement must be sent to one of the COSC labs where it immediately goes through the following: tests the numbers engraved on the movement (in relation to the list supplied by the applicant), the movement is placed in a 5-slot clasp, the movement is wound according to the brand’s supplied guidelines, and the parts are placed in a temperature controlled enclosure for 12 hours at exactly 23°C.

Then, over the next 15 days, the parts of the wristwatch go through daily tests. Each day, the clocks and watches are measured and reassembled. At the end of that time period, the wristwatches are judged by seven different criteria: average daily rate, mean variation in rate, greatest variation in rate, the difference in rates in horizontal and vertical position, largest variation in rate, and variation in rate depending on temperature and rate resumption. If the watch passes these guidelines, it is officially awarded the certification.

All COSC-certified watches are subject to a battery of tests

3. The COSC doesn’t just measure mechanical wristwatches, they also measure pocket watches, fixed time devices such as onboard instruments and carriage clocks, and quartz timepieces. There is currently no international standard for measurement of a watch with a quartz oscillator, so the one used by the COSC is based on the same ISO 3159 standard used in their measurement of mechanical wristwatches.

4. Over 1.6 million watches are certified every single year, a figure that has grown substantially over the decades. In 1976, when the current iteration of the COSC was founded, only 200,000 watches passed the exam. Fast forward to the year 2000 and there were one million chronometers that completed the exam. Out of all watches exported from Switzerland, only 6 percent are COSC certified. Out of all mechanical Swiss watches that are exported, 21 per cent are COSC certified.

5. According to a report from 2015 — which is the last year that the COSC will publish the exact figures citing a request from the brands to protect their confidentiality — the three companies that receive the most COSC-certified timepieces aren’t all that surprising. Rolex is numero uno with 795,716 watches, Omega is second with 511,861, and Breitling is third with 147,917 total timepieces (28,499 of those are quartz models). Next up are two of the more accessible brands in the Swatch Group, Tissot (96,563) and Mido (49,962).

There’s a sharp drop off in total number for the rest of the top ten with Tudor (23,003), Chopard (16,107), Zenith (6,824), Panerai (6,262), and Bremont (5,860) rounding it out. Ball Watch Co. (5,031), Carl F. Bucherer (4,577), Titoni (4,146), Christopher Ward (3,362), and Ulysse Nardin (2,561) make up the next five. However, there is no way of updating these figures to see how the production of COSC certificates has changed in recent years.