50 years after the international ISO 3159 Standard for what is a precision chronometer came in power, COSC is bringing its testing to watch lovers in places like Watches and Wonders. Its goal is for you to understand what a real chronometer is, and what stringent testing it must endure. But first, let’s make a quick recap about what a COSC standard certification is. It means that the movement of your watch is tested in 5 positions, and the accuracy must be within -4 to +6 seconds per day. This precision must be achieved during a 12-20-day testing period at three different temperatures: 8°C, 23°C, and 38°C. Since 1973, COSC – Contrôle Officiel Suisse des Chronomètres (the Official Swiss Chronometer Testing Institute), has tested around 57 million movements. As the ISO 3159 is a truly international standard, other countries have their own independent, third-party testing organizations, since COSC only works for the Swiss watch industry.
At Watches and Wonders 2026, COSC brought its expertise to the people, which was a very appreciated part of the LAB projects, a space dedicated to innovation and cutting-edge technologies. Here visitors became participants. With an electronic Teslascope Pulse device, they could test the precision of their own watches. What was also a wake-up call for many a visitor was the adverse impact of magnetism on a watch movement. This was seen when testing a watch, followed by demagnetizing, and then testing it again. So, unless you want to go to a watch dealer for magnetizing, watch out for those phones, speakers, computers, and TVs, unless your watch run on non-ferocious materials or is equipped with a faraday cage.
The direct effect of different position also gets fascinating when you can experience it as it happens. Gravity’s effect on the running of the movement is tested using a so-called Witschi device. And the balance spring never behaves the same way in different angles. This is why the testing period has to be so long – and the long-duration measurement made by CISC is always made with an optical camera, as this is the best secure way to validate precision at this level. At the end of the day the watches must meet seven strict criteria including the aforementioned precision of -4/+6 seconds per day, in order to be given the Chronometer Certified title.
During COSCs public presentations the audience is also able to sit down at the bench and try the craft of a watchmaker by doing hands-ion adjustments: What better way could there possibly be to understand how important the tiniest regulation is?
During the exhibition many people were also positively surprised to learn that COSC is a non-profit, public interest organization. And in 2026 COSC – in order to answer a growing demand in the market of Swiss watches – also started to offer a more advanced precision of -2/+4 seconds per day, while also testing magnetic resistance up to 200 Gauss, and verifying the stated power reserve. Last but not least, there is one big difference with the new, additional five-day test referred to as COSC Excellence: With COSC it is just the movement that is tested, but for COSC Excellence the whole watch is tested during the additional days. These tests also include robotic machinery that closely simulate conditions that closely simulate real-life wear.
If this is important? Well, after conducting a survey with the visitors to COSC during the exhibition, 92% consider independent certification to be an essential reference point when choosing a watch.
Oh, you missed COSC during at Watches and Wonders? Don’t worry, you will soon have another chance. At Geneva Watch Days, which in 2026 takes place from September 2-6, COSC will be in the lakeside pavilion welcoming visitors again.
