The COSC Releases Excellence Chronometer, its New, Stricter Standard in Chronometry
What is a chronometer? In short, it is a watch that has been officially tested for its precision. And to guarantee the precision of watches, several tools exist, such as the ISO 3159 standard and official organizations like the Observatoire de Besançon in France, the Glashütte Observatory in Germany, the Japan Chronometer Inspection Institute, or the recently created Geneva Observatory. For over 50 years, the leading authority in this context has been the COSC or Contrôle Officiel Suisse des Chronomètres, created in 1973. Now, as teased in an interview with its CEO, Andreas Wyss, the COSC raises the bar and establishes a new standard in Swiss chronometry, with the COSC Excellence Chronometer. More stringent, with new testing procedures (magnetic fields, power reserve, real-life wear…), it is said to take into account how watches have evolved over the past half-century. Better? Sure. Perfect? Let’s take a closer look.
The COSC, its competition, and how it became slightly obsolete
For over 50 years, the COSC or Contrôle Officiel Suisse des Chronomètres has been the main organ to certify watches for their precision and to grant them the title of chronometer. In recent years, however, the certification environment has drastically changed. Many new organizations have been created with more stringent testing procedures than the COSC's ISO 3159 standard. Additionally, the life of mechanical watches has evolved, with greater exposure to magnetic fields, longer power reserves, new materials, and more intensive daily wear.
To put things into perspective, the COSC is not the only organization capable of officially certifying watches and granting them the title of chronometer. While it remains the leading organization, particularly for Swiss-made watches, major competitors have emerged in recent years. Besides traditional organs like the Observatoire de Besançon, the Glashütte Observatory, the Japan Chronometer Inspection Institute, or the Geneva Observatory, the COSC has faced pressure from impressive alternatives, primarily the Master Chronometer certification created in 2015 by Omega and now used by Tudor.
A chronometer is a watch tested according to the ISO 3159 standard for 'Timekeeping instruments – Wrist-chronometers with spring balance oscillator'. A certified chronometer goes further, being certified by a third party, such as the COSC or another official authority. The COSC conducts a series of tests over 15 days, operating independently, with watch manufacturers sending movements to one of its facilities. The checks include static tests performed in the laboratory, with each movement/watch undergoing a battery of tests specific to each of the four types, for several consecutive days, in five positions, and at three different temperatures.
In summary, the COSC measures seven criteria, including the well-known average daily rate of -4/+6 seconds per day. This alone is not sufficient to make a watch a chronometer, but it provides a solid indication of what to expect.
In recent years, initiatives like the Master Chronometer, jointly developed by Omega and METAS, have raised the bar of certification to a new level. Notably, in addition to stricter deviation standards (0/+5 seconds per day, twice as precise as COSC), Master Chronometer includes testing movements and full watches to extremely high magnetic fields (up to 15,000 gauss), as well as testing water-resistance, durability, and power reserve.
Other initiatives exist, such as Qualité Fleurier, which adds several quality criteria to the initial COSC certification, or the Poinçon de Genève, now part of TIMELAB. However, many large Swiss brands have developed their own internal certifications. The official chronometer certification by an independent organ remains a prerequisite, but brands add more stringent criteria. For instance, Rolex's Superlative Chronometer certification accepts daily deviations of -2/+2 seconds per day. Omega has recently presented the Laboratoire de Précision, a new chronometer certification open to all brands, officially authorized by SAS. Finally, Patek's internal Seal guarantees a remarkable precision of no more than -1/+2 seconds per day.
All of this to say that the older COSC certification felt outdated compared to the competition. And it may not align with current expectations.
The mission of the Contrôle Officiel Suisse des Chronomètres (COSC) remains unchanged; it is an independent organ to test the precision of Swiss-made watches through a neutral, independent, and rigorous method. However, with the rapid evolution of the competitive environment and changing expectations of brands and clients, the basic 'Certified Chronometer' standard is no longer sufficient. Yet, this first level of certification will continue to exist as a hallmark of performance, but brands now have the opportunity to climb one step higher with the new Excellence Chronometer certification.
So, what is this Excellence Chronometer certification all about? In short, it involves more stringent precision standards and the addition of criteria to make the certification relevant in today's context. According to COSC, it will feature a daily rate tolerance of 6 seconds instead of 10, magnetic resistance up to 200 Gauss, and verification of the stated power reserve. Additionally, watches will be tested under conditions that closely simulate real-life wear.
The new certification builds upon the COSC's Certified Chronometer certification, based on the seven criteria of the ISO 3159 standard. Once certified, movements return to the manufacture for casing, and complete watches undergo five additional days of evaluation. Using a robot to simulate average wrist wear, the watch's precision is tested under semi-dynamic conditions for 24 hours. This is followed by a measurement where the average daily rate must fall between -2 and +4 seconds per day (instead of -4 and +6 seconds per day for standard COSC certification). While it's better than the previous standard, it's still far from what brands like Rolex or Patek Philippe offer, and it gets closer to the Master Chronometer certification.
The COSC is not setting even more stringent standards due to the complexity of regulating mechanical watches to a daily rate tolerance below 3 to 4 seconds. Such a criterion could potentially eliminate many entrants, such as watches with outsourced movements from Sellita or other third-party movement makers. It's not impossible, but it requires large investments in precision manufacturing.
Next, the watch is exposed to a 200 Gauss magnetic field while maintaining its performance. This level of magnetic resistance must be compared to industry standards. The ISO 764 or its equivalent DIN 8309 specifies a watch must resist a direct current magnetic field of 4800 A/m, which corresponds to about 60 gauss. A new version of the ISO 764 standard, published in 2020, sets a resistance to direct current magnetic field equal to or higher than 16,000 A/m, which corresponds to about 200 gauss, exactly what the COSC uses in its new Excellence Chronometer certification.
However, the environment has changed drastically over the years. Rolex's Milgauss model, designed for scientists working with magnetic fields, could resist fields up to 1,000 gauss in the mid-1950s. IWC's Ingenieur 3508 in 1989 could withstand magnetic fields of up to 500,000 A/m. The Master Chronometer certification tests watches up to 15,000 gauss. In our day and age, we are surrounded by magnets, and many brands now add magnetic-resistant hairsprings made from silicon or Nivachron in their movements.
On one side, we can only applaud the COSC for delivering a new and stricter standard with its Excellence Chronometer certification. Precision is key to mechanical watchmaking, and the COSC's new chronometer standard of -2/+4 seconds per day is certainly great news. The fact that the COSC now tests complete watches and not just movements makes the testing process more relevant, as the classic chronometer certification tested only movements. The simulation of wrist wear is a great addition.
However, it's not enough. Modern mechanical watches require greater magnetic resistance, quality, origin of parts, and craftsmanship. The COSC's Excellence Chronometer falls short compared to the rest of the industry in these criteria.
The COSC's Excellence Chronometer certification has already been integrated into the organization's environment, and in March 2026, the first pilot tests will be conducted in COSC laboratories to validate procedures and support brands through this adjustment phase. Starting in October 2026, deployment begins as brands fully enter the new process, and the first watches certified under these redefined standards will start to emerge.
For more information, visit www.cosc.swiss.
