COSC. Four letters you’ve likely spotted in a watch’s name or specs, but you’re not entirely sure what it means. Don’t worry, none of us knew once-upon-a-time either. So, what is it? What does COSC mean in watches? And is COSC important? Let’s embark on a journey to reveal all the secrets behind COSC certification and discover some of the timepieces that have been able to attain it.
What does COSC stand for?
COSC stands for "Contrôle Officiel Suisse des Chronomètres," which ultimately translates to the Swiss Official Chronometer Testing Institute. Essentially, the independent organisation is responsible for testing and certifying the accuracy of high-precision watch movements. The institute places each watch under a rigorous testing schedule to evaluate their precision and performance. If it passes, the watch is COSC-certified and can be called a ‘chronometer’.
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What are the requirements for COSC-certification?
As you can probably imagine, COSC-certification isn’t easy to acquire. The institution doesn’t just take a watch movement and monitor its accuracy on a flat surface in mild conditions. The testing is a little more brutal than that. At the end of the day, a COSC-certified watch is designed to be able to keep up with you, no matter whether you’re a laid back 9-5er or someone with an adventurous spirit.
The process begins with the movement uncased and tested for a total of 15 days in five positions (3 o’clock, 6 o’clock, 9 o’clock, dial on top, dial on the bottom) and at three different temperatures (— 8°, 23°, and 38°C). The movements are kept at each temperature and in each position for 24 hours and tested on their accuracy. Once the mechanism has been tested in every position and temperature, the results are compiled and must meet the following seven criteria. COSC enforce their stringency by stating the requirements below are considered absolute limits and no calculation result is rounded up or down.
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- The average daily rate needs to be between −4 and +6 seconds.
- The mean variation in rate for the entire period is 2.
- The greatest variation in rate for any two-day period is 5.
- The difference between rates in horizontal and vertical positions is −6 and +8 seconds.
- The largest variation in rates is 10.
- Temperature variation allowed is +/- 0.60.
- The rate resumption must be +/1 5.
Is COSC-certification Important?
The importance of COSC-certification varies between wearers. While some understandably believe the accuracy of a timepiece is fundamental, others may prefer to focus on other aspects of watchmaking such its design, history, price or complications. Chronometer-certification is something worth taking note of however, as it remains an important factor to consider when evaluating a watch’s quality.
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For many collectors, a COSC-certified movement signifies a manufacturer’s dedication to precision and craftsmanship, which is likely to be reflected across other elements of the design too. Ultimately, you have a guarantee that the movement housed inside your watch is reliable and accurate, and when serviced regularly, it should provide you with precise timekeeping for a lifetime.
COSC-certification can also add value to a watch so if you are looking for an investment timepiece, choosing a chronometer watch is a good place to start. Only around six percent of all Swiss watches are certified by COSC so that alone places you in an exclusive group of watch owners. Last but not least, COSC-certification also helps disband any worries about authenticity. Contrôle Officiel Suisse des Chronomètres is part of the Federation of the Swiss Watch Industry’s anti-counterfeit group and stamps each movement with a unique number and a certificate to verify its legitimacy.
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Popular Chronometer Watches
Due to the standards chronometer watches must meet, they often run a little higher in price to their non-certified counterparts. That’s not to say, however, that you can’t find COSC-certified watches at a reasonable price. We have already created a run down of our top 5 best chronometer watches under £2,000 here for those interested.
Some of the most affordable chronometer watches include the Formex Essence Thirty-Nine and the Christopher Ward C65 Aquitaine Bronze, both of which run off the Sellita SW200-1 chronometer-graded movement with a 38 hour power reserve. Other well-priced chronometers include those engineered from BALL Watch Company, like their Engineer III Marvelight and Engineer Hydrocarbon NEDU. The DOXA Sub 300 Carbon COSC is another fantastically affordable chronometer, especially for those that enjoy underwater exploration.
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In terms of popularity, luxury watch brands like Rolex and Breitling are responsible for creating some of the world’s best-selling chronometer watches. In fact, both these manufacturers sell only COSC-certified watches. Rolex takes this one step further and has a certification of its own called “Superlative Chronometer” which attests to providing an accuracy of -2/+2 seconds per day – but that’s a whole other article for another day!
Despite COSC-certification not being the easiest of accreditations to obtain, there are still several chronometer watches on the market to choose from, differing in design, functionality and affordability. We’d love to know what your favourite chronometer watch is, and if you own one, which did you choose? Let us know in the comments below!
