ntering one of the COSC’s three laboratories is not easy. Before reaching the laboratory proper, you first of all have to pass through a series of strictly controlled buffer spaces. At first glance, nothing marks it out as a place where movements are tested for precision. The impression is rather of one vast, ultra-high-tech space where silent operators go about mysterious tasks.

Approach the windows and you realise that this space is a building in its own right, inside another building like a second skin, insulated completely from the outside. “Here, static electricity is absolutely prohibited,” Andreas Wyss, COSC director, explains. “The movements must not be subjected to any outside influence. Also, we have to maintain atmospheric overpressure, which we measure continuously. External sensors on the roof of the building enable us to regulate the pressure by adding a few hectopascals via windsocks.”

“The ambient air is continuously monitored by numerous sensors in all the rooms the movements move through. The temperature, humidity, dust, atmospheric pressure and dew point are measured continually every minute, 24 hours a day and 365 days a year,” he goes on.

The COSC has three such laboratories, all strictly identical, at Biel, Le Locle and Saint-Imier. “It’s a matter of security,” we are told. “To deal with any major failure, but also to be able to respond immediately to any sudden surge in demand from our customers, the premises we occupy are oversized. And in the event of a prolonged interruption of work in one of them, the two others would be able to absorb all the timepieces awaiting certification until the defective laboratory came back into production.”

Each of these laboratories also uses an identical time base of three atomic clocks, two of which are synchronised to GPS time and the third to the DCF signal (a radio wave time transmission system driven by a caesium atomic clock, which provides atomic time with a margin of error of one second per million years). These three clocks have to be synchronised to the nanosecond “so that time can be distributed across the testing machines”.

Confidentiality guaranteed

Of the “raw material” that feeds this laboratory – the movements (and more rarely, watch heads with the movement fitted) to be tested – we see not a single example in the open.The customers bring along their batches already packaged up and collect them once tested. The COSC plays no part in the transport for obvious reasons of the damage that could occur beyond its strict responsibility for testing. Each client has their own login, and the gate and laboratories are compartmentalised to guarantee confidentiality.

The timepieces, fitted with a neutral working dial, are then placed in special containers; an optical reader tests their engraving, then they are wound by machines specially calibrated in accordance with the type of movement and the exact number of revolutions required to wind them. They are then put through a 15-day cycle and daily tests, all automated and fed into a shared database specific to each movement tested.

On day zero, the calibres, arranged in batches, are placed in a chamber at 23° for at least 12 hours to stabilise them before the round of tests begins. Every 24 hours, they are removed from the chamber, measured, rewound and returned according to a cycle of five different positions: 3 o’clock, 6 o’clock, 9 o’clock, dial up, dial down.

Each phase, each operation and each repositioning of every one of these calibres is noted, measured and compiled on an electronic tablet. In other words, they are tracked to the nearest second, including who did what, and the data is kept by the COSC for ten years.

The timepieces under continuous control spend time in three different chambers monitored by temperature and humidity sensors for 13 days at 23°, one day at 38° and one day at 8°.

Less than CHF 10 per movement tested

Seven criteria are measured according to the ISO 3159 standard, along with the tolerance data in seconds per day for a balance spring movement or wristwatch.

“We test seconds and so we only test watches that display them. Without a seconds display, the end customer can’t check the watch’s precision,” Wyss explains, adding “Since 2023 we’ve also been able to test complete watch heads semi-automatically, whereas for movements the process is fully automated. But the process for watch heads takes longer, and to tell the truth watchmakers don’t like it too much. If a watch fails, they have to start all over again because the word Chronometer is engraved on the dial. But we’re working on it. We also certify quartz watches, admittedly in limited quantities, as well as pocket watches and clocks. It’s not possible to certify solar watches because their energy source is variable by definition. And as for simple chronographs, they can’t be certified as chronometers, because the purpose of a chronograph is to measure short intervals of time for particular events. As things stand today, there is no standard certifying the precision of a chronograph. On the other hand, high-precision watches with a chronograph function can be certified chronometers. As can complicated watches, like tourbillons for example, but still only on condition that the movements display seconds.”

And how much does certification cost? “We do series of one to 500 timepieces and the price, which is identical for all our customers, comes to less than CHF 10 per movement tested. If manual testing turns out to be required, it can cost up to CHF 100.”

Repositioning the COSC “brand”

The general public often confuses the notion of “chronometer” with that of “chronograph”. Does COSC certification, the French acronym for Official Swiss Chronometer Testing Institute, really add value to the watches it certifies? Does calling a precision watch a “chronometer” mean anything to the public at large? Is it still a selling point?

“I think that today, the notion of brand has become more important than that of precision,” says Wyss. “And the real added value of certification is important mainly for small and medium brands. But you have to see the bigger picture. The COSC is a non-profit association recognised by the Swiss Confederation, set up by the cantons of Geneva, Vaud, Neuchâtel, Bern and Solothurn. For 51 years this year, we’ve had the same statutes, no shareholders, we receive no subsidies, we’re fully self-financing. This neutrality and independence is our great strength.”

“Our other great strength is that we’re the only body in the world capable of scientifically processing very high volumes of calibres – today up to 2.3 to 2.5 million movements per year. It’s absolutely unique worldwide, and that plays a huge role in the image of Swiss watches. It’s also a guarantee of their quality. But it’s true that in relation to the general public we’ve always been much too discreet. We need to reposition the COSC brand, make people more familiar with what the COSC is…and the difference between a chronometer and a chronograph.”

To this end, taking advantage of its 50th anniversary in 2023, the COSC launched a campaign and commissioned a book with a novel theme: the social and economic history of chronometry (Histoire sociale et économique de la chronométrie, published by Alphil), the writing of which it entrusted to the expert hand of historian Pierre-Yves Donzé. Starting with the beginnings of chronometry in the 17th century, the work describes how “the precision of mechanical watches became a commercial issue” (1860-1890), discusses at length the “Golden Age of chronometry” (1900-1970) before chronicling the somewhat turbulent foundation of the COSC in 1973 and its history to date, including the “luxury revolution” which has led to an escalation in the number of brands submitting watches for certification.

The book provides the key to a better understanding of how and why the quest for chronometric precision and certification have gone hand in hand with the economic, social and cultural development of watchmaking and continue to play an active role in it. In parallel, a study on the COSC’s image was launched in the relevant circles.

The stakes of certification

As proof that chronometric certification remains an important issue – in relation to economics, in relation to image – initiatives surrounding it are proliferating. Apart from the COSC, until recently virtually the only other certifying bodies were the Besançon Observatory in France, with its Viper’s Head stamp, and the Wempe laboratory in Glashütte, Germany. In Japan, after submitting some movements to the COSC for testing – but without requesting official certification – Grand Seiko took inspiration from its methodologies and now subjects its calibres to even stricter chronometric testing. Elsewhere, quality stamps such as the Fleurier Quality Foundation seal include COSC certification among their prerequisites. But initiatives are being hatched to break free.

The most prominent example is Patek Philippe, which in 2009 decided to forgo all external certification (including the Geneva Seal) and do its own, fully independent certification, applying criteria covering the case and decoration in addition to the movement, its finishes and its chronometric precision, measured after casing-up. In other words, stricter than the COSC criteria, with a tolerance of -1/+2 seconds a day compared with the COSC’s -4/+6. But do you have to be one of the big names to have the luxury of doing that?

Rolex, another giant of the watchmaking world, does indeed have its own certification, called Superlative Chronometer. But as far as precision is concerned, this is “complementary to official COSC certification” of its movements. The final tolerance requirement is around -2/+2 seconds. Until recently, the only reliable source for the number of chronometer watches produced by Rolex every year were the annual, nominative statistics published by the COSC. For example, it was possible to learn that in 1998, Rolex had had exactly 631,129 movements certified, 77.4% of the total for that year. A few years ago, it politely asked the COSC to cease such transparency – proof, if proof were needed, that certification is as important as ever.

In 2008, the Canton of Geneva set up the private foundation Timelab, tasked with delivering the famous Poinçon de Genève, or Geneva Seal (which certifies craftsmanship, not movement precision), and chronometric certification via the Geneva Chronometry Observatory (the Geneva Astronomic Observatory was founded in 1774). While Timelab represents an alternative to the COSC and bases its certification on the same standard, ISO 3159, this Geneva-based laboratory, which delivers a mere 5,000 certificates a year, still needs to make itself better known. (On this, read our detailed article Timelab perpetuates Geneva’s horological reputation, on europastar.ch) But only recently, another announcement caused further upset in the certification world: in April 2024, Omega issued a press release announcing the creation of a “Laboratoire de Précision, for in-depth chronometry trials”.

Andreas Wyss, whom we met the day after this announcement – an appointment made a long time beforehand – still seemed shaken. Not so much by the news itself than by the fact that he had learned of it in a phone call from a journalist who had received the press release. Omega explicitly stipulates that this Laboratoire de Précision wishes to be “completely neutral and independent, offering chronometric testing opportunities for all brands and movement manufacturers. It is an alternative officially authorised by SAS (the Swiss Accreditation Service), like the COSC, to carry out alternative and independent testing.”

Put bluntly, Omega, which already had its METAS certification but continued to have batches tested by the COSC, is now a direct competitor. What’s more, it takes a couple of swipes at the COSC in the process, stating that it intends to “go much further than today’s industry standard” with tests that are “extremely comprehensive, and most importantly, continuous throughout all 15 days – unlike the current method, which only takes precision measurements every 24 hours”. A head-on attack. In the same breath, Omega announces the construction of two dedicated chronometric testing sites of more than 1,000m2, in Biel and Villeret.

But there’s a but. Omega goes on to talk above all about improving the precision of its own movements. Which prompts us to ask: will third-party brands dare entrust to Omega – a dominant, competing brand – the task of certifying and rating their own “chronometers”? The history of chronometry, the COSC and the certification stakes is far from over.