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For anybody new to the world of watches or taking it upon themselves to discover more about the finer aspects of horology, you may have noticed a four-letter word appearing across the websites and throughout the marketing of many watch brands worldwide: COSC. But what does this acronym stand for, and why is it important in the world of watchmaking?

COSC, or the Contrôle Officiel Suisse des Chronomètres, is a Swiss-based institute that tests Swiss-made mechanical or quartz movements for accuracy – hence its translated name, the Official Swiss Chronometer Testing Institute. If horology is centred around the pursuit of the highest precision, then the chronometer is the holy grail of watchmaking: a mechanical chronometer must fall within a tolerance of -4/+6 seconds a day, while a quartz version is accurate to a sublime +/- 10 seconds a year.

It’s the job of the COSC to ensure that the movements it receives from brands around the world meet the tolerance requirements expected of a chronometer (something also established in ISO 3159 by the International Organisation for Standardization). The COSC is the only place that can certify a watch or movement as chronometer standard – this comes in the form of a certificate of authenticity, specific to the movement itself. While there are other grades of mechanical (standard or elaboré) and quartz movement (it’s worth noting that either type can become a chronometer, as this refers to the accuracy of its timekeeping, rather than any special parts or design that would give it such status), the chronometer is the zenith of fine watchmaking. In that sense, the COSC holds the task/privilege of ensuring this artform continues to operate at the lofty levels that have so deservedly seen it classed as one of the pinnacles of human achievement.

Out of all Swiss-made watches exported from the country, only 6% are COSC certified. For anybody receiving a COSC-certified watch, the certificate of authenticity they receive with their watch is the culmination of the process between COSC and its manufacturer.

COSC certificate

Split between three separate testing facilities in Switzerland (Biel, Saint-Imier and Le Locle, in case you were wondering), the COSC operates seven days a week for the majority of the year. This is a necessity to meet the burgeoning needs of the Swiss watch industry: while 200,000 movements were originally submitted when COSC’s current iteration was founded back in 1976, in 2015 alone that number had rocketed to over 1.6 million. While you might rationally think this surge in demand for accuracy is the result of an increasingly well-informed watch-buying public (thanks, the internet), you’d be surprised: out of all Swiss-made watches exported from the country, only 6% are COSC certified.

And that raises another point: for a watch to be eligible for COSC certification, it needs to be Swiss-made. While regulations have long been in place to protect the quality and integrity of many Swiss exports, 2017 saw the introduction of stricter new Swiss-made criteria for watches:

• At least 60% of the production costs of a watch taken as a whole must be Swiss-based;
• The movement must still contain at least 50% Swiss-made components in value (not in quantity) and at least 60% of the movement’s production must be generated in Switzerland;
• The technical development of a ‘Swiss Made’ watch and movement must be carried out in Switzerland.

It’s simple: if a watch doesn’t fulfil each of the points above, it can’t carry ‘Swiss made’ on its dial. (That’s why, even though every new Christopher Ward release is designed at our Maidenhead HQ, their production takes place at our Swiss atelier in Biel – just over a mile away from one of COSC’s testing facilities, in fact – thus ensuring their Swiss-made status.) It’s a clever move by the Swiss: by keeping COSC certification exclusive to their own watches, they’ve neatly managed to position themselves as a nation synonymous with quality and world-class timekeeping.

The COSC’s rigorous testing procedures only reinforce this commitment to the utmost accuracy. For anybody receiving a COSC-certified watch, the certificate of authenticity they receive with their watch is the culmination of the process between COSC and its manufacturer. An initial list of movement numbers is supplied by the latter, which a member of the COSC team will then check has been engraved onto each respective movement. Each is then wound in accordance with the manufacturer’s instructions, and then placed into a 5-slot clasp. This clasp is then moved to an enclosure that is gradually raised to 23°C (± 1°C) over a 12-hour period before the testing procedures begin.

The duration of these tests take depends upon the type of watch in question. A wristwatch or pocket watch undergoes tests for 15 days; larger clocks can take 19; meanwhile quartz-powered instruments will remain under examination for 13 days. Once each movement has been tested in a variety of positions and conditions, it is judged upon seven different criteria: average daily rate (essentially the gain or loss in seconds per day), mean variation in rates, greatest variation in rates, the difference between rates in horizontal and vertical positions, largest variation in rates, variation in rate depending on temperature and rate resumption. If each falls within COSC’s specific guidelines, the movement can be awarded the certification you receive with your COSC-certified watch, its specific test results detailed on the respective paperwork.

So, is the COSC important? It depends who you ask. For anyone who admires the aesthetics of a watch, but isn’t as concerned with the absolute accuracy of the watch on their wrist, the extra money associated with sending a movement off to Switzerland isn’t as crucial to their enjoyment and experience (non-chronometer-certified movements can fall within chronometer-certified tolerances, after all – there’s just no documentation to acknowledge this). Yet for anybody who sees their watch as more than an item of jewellery, but as a piece of engineering that exemplifies humankind’s technological progress since the days of the sundial or hourglass, the COSC single-handedly preserves the highest forms of precision watchmaking. You might have to pay a little extra for it, but to have the guarantee of world class precision, wherever you go? Priceless.