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Watches & Their Precision: Chronometry Certifications

Le 28 January 2016

Let’s talk today about chronometry precision, a vast subject that often times is at the heart of passionate discussions. There was a time many centuries ago when precision and reliability of a mechanical watch was vital for navigators, aviators and great explorers. Indeed, geographic coordinate calculations and the knowledge of your exact location relied upon the precision of your chronometer. Just imagine how important that information was during the era of the discoveries of the American continent…

Today, the chronometric precision of our mechanical watches isn’t vital anymore, far from it actually. If you miss the beginning of your lunch break because of a slow watch, your smartphone will keep you on track, followed closely by the breakroom microwave. But that’s not the point. As everyday adventurers, we enjoy putting ourselves in danger but relying solely on our little mechanical heart in order not to miss that Tinder rendez-vous that could change our lives, like Christopher Columbus discovering the New World.

Certifications Seamaster 300 - Cosc

All jokes aside though, where are we at today? What means do we have to check the precision of our timepieces and what certifications are out there? These are questions which we’ll answer today.

Chronometric precision :

A mechanical watch’s chronometric precision is measured with the help of different instruments, and can be expressed by different indicators. The most explicit and frequently used method to define a level of precision is in fact through the watch’s imprecision by measuring the loss or gain of time. We express this method by seconds/day.

Today, certain professional portable measurement instruments, which come in handy, are able to give you this information in barely a dozen seconds, with exceptional reliability. We tested one a few weeks ago, the ONEOF Accuracy, which revealed several surprises within our watch cases.

While we’re at it, it’s worth noting :

“Chronometric norms measure the precision and reliability of a movement in various conditions: Yes. What about a movement within a watch case? They do as well. But chronometric norms mainly determine a watchmaking brand’s capacity to refine its quality control as well as its ability to deliver well-regulated movements.”

If we come full circle with our reasoning, another way of putting it is that a good watchmaker should be able to regulate any movement so that it conforms to the highest chronometric norms, any time, in any position. And this is where it is important to be aware of the different certifications, and the conditions and measurements that each one of them implies.

A few Chronometry Certifications to know :

Official Swiss Chronometer Testing Institute COSC (Switzerland)

Certifications Rolex - cosc

Founded in 1973 under its current structures, the Official Swiss Chronometer Testing Institute, or COSC for short, was created by five watchmaking cantons (Berne, Geneva, Neuchâtel and Vaud) along with the the Swiss Watchmaking Industry Federation. It regroups laboratories which had been established independently one by one towards the end of the 19th century. However, this certification is only open to Swiss watches, as watchmaking is one of the crown jewels of Swiss industry. Many Swiss brands have their movements certified “chronometer” by the COSC. The brands which manufacture the most certified movements per year are Rolex and Breitling, who send almost all of their production line to be certified, but other references such as Tag Heuer, Zenith and many others also are heavily certified…

Take note that this certification only concerns the movement and not the watch as a finished and packaged product… we’ll come back to that in a moment.

    • Acceptable variations: between -4 and +6 s/d
    • Number of measurements: Over a 15 day period, the watch is evaluated in 5 different positions and at 3 different temperatures.


  • Conditions: In order to receive the COSC chronometer certification, the movement must meet 7 different criteria, among them the average diurnal rate, acceptable variations in horizontal and vertical positions, and its precision under thermal variations.

Besançon Observatory Chronometric Certificate (France)

Quite similar to the COSC tests, the “viper’s stamp” is one of the most arduous chronometric certifications. In order to obtain the General Bulletin Order according to the ISO 3159 norm, the tests the watch has to undergo are the following:

The precision of the watch is evaluated over a 15 day period in 5 different positions and at 3 different temperatures. Founded in 1885, the Besançon Observatory, the cradle of French watchmaking, was comprised of 3 services: astrological, meteorological and chronometric. One of the legitimate non-Swiss references in terms of chronometric certification. Lesser known by the general public, but appreciated by the true connoisseurs. Dodane, the French manufacturer of aviation chronographs certifies their movements here, along with several illustrious independant Swiss watchmakers (Kari Voutilainen for example…)

Certifications Observatoire Besancon Voutilainen

    • Acceptable variations: between -4 and +6s/d
    • Number of measurements: Over a 15 day period, the watch is evaluated in 5 different positions and at 3 different temperatures.


  • Conditions: The movement is evaluated based on 7 criteria, separated into 3 categories: the average diurnal variation, the average variation from period to period and the error of compensation per degree celsius. So the seven criteria are the average diurnal rate, the average working variations, the largest working variation, the difference between horizontal and vertical, the largest working difference, the thermal variation and the rate correction.

Grand Seiko Norm (Japan)

In its perpetual quest for precision and watchmaking prowess, the Japanese manufacturer decided to function according to its own precision standards: the Grand Seiko norm. This norm, which Seiko imposes on all of its mechanical production, is one of the most strict and refined. Acceptable working variations are even more limited than the previous two certifications… The expectation of the Rising Sun.

Certifications Grand Seiko

  • Acceptable variations: between -3 and +5s/d
  • Number of measurements: Over a 17 day period, the watch is evaluated in 6 different positions and at 3 different temperatures.
  • Conditions: Two additional days of tests for a 6th additional position. The movement will also be evaluated based on 7 criteria, separated into three categories, just like the COSC and the Besançon Observatory.

Additional certifications :

After having successfully passed the COSC tests, Swiss chronometers can undergo additional certification tests, evaluating their anti-magnetic resistance or their esthetic as well as the degree of quality and finish of the assembled watch as a whole.

Metas Chronometric Certification (arduous anti-magnetic testing)

Certifications Omega Master Chronometer

Developed in 2015, the METAS independent certification the youngest child of timepiece certifications. This certification adds to the usual tests a test verifying the functionality of the watch when it is exposed to intense magnetic fields of up to 15,000 gauss. At the end of these tests, if the watch passes them all, it will then be certified Master Chronometer. Omega’s Globemaster Co-Axial Master Chronometer was the first watch to have received the certification.

This certification is open to any Swiss watch having obtained the COSC certification. These requirements not only test the movement but also the assembled watch as a whole in real conditions…

  • Obtaining the Metas certification is based on 8 criteria: the average daily precision of the watch, the functioning of the COSC-certified movement while exposed to a 15,000 gauss magnetic field, the functioning of the watch (completely assembled) while exposed to a 15,000 gauss magnetic field, the daily precision variation after being exposed to a 15,000 gauss magnetic field, the waterproofness of the watch under real conditions, the reliability of the power reserve, the variation of the power reserve between 100% and 33% and finally the working variation of the watch in 6 different positions at 23 and 33 degrees Celsius.

The Fleurier Quality Foundation Certification (evaluation of finished watches)

Created the 5th of June, 2001 and inaugurated the 27th of september, 2004, this certification born from a communal project between Chopard, Parmigiani Fleurier, Bovet Fleurier and Vaucher manufacture Fleurier, all of them from the Val-de-Travers region in the Neuchâtel canton in Switzerland.

It’s the first watchmaking certification evaluating the finished watch, as it is when it enters the market. Of course, this is aiming more for the high-end spectrum of Swiss watchmaking production. A trustworthy quality guarantee…

We hope we were able to elucidate this often times obscure world of chronometric certifications and to put their importance into perspective. One certain is that if these norms certifications keep on developing, it would be interesting for them to focus more and more on finished watches. Many things can happen between the testing of the movement and its casing… The Metas and Fleurier Quality certifications are without a doubt the first big step forward, despite only being available to Swiss watches. Gentlemen, why not play with our German and Japanese counterparts?