FAQ

The COSC, or the Official Swiss Chronometer Testing Authority is a non-profit public interest association founded in 1973. Its mission is to certify the precision of Swiss watches as chronometers. The COSC encompasses the laboratories that were originally created independently of each other as early as the late 19th century. Today, it operates across three monitoring sites in French-speaking Switzerland, in Bienne, Le Locle and Saint-Imier, and is coordinated by a management team based in La Chaux-de-Fonds.

A COSC movement refers to a watch movement that has been certified by the Official Swiss Chronometer Testing Authority (COSC) as a chronometer. This certification attests to the high precision of the movement, whether this is mechanical or quartz. To obtain this certification, the movement must pass a series of rigorous tests that assess its precision under different temperature and position conditions. The mechanical movements are tested in accordance with the ISO 3159 standard, while quartz movements follow internal requirements inspired by this standard but adapted to their specific features.

The COSC is a guarantor of high precision and quality for a watch. When a watch is certified by the COSC, it receives the official designation of “chronometer,” meaning that it has passed a series of rigorous tests to verify its precision. These tests are based on strict criteria defined by the ISO 3159 standard for mechanical watches, and internal requirements for quartz watches. The COSC certification is a guarantor of expertise and reliability, enabling manufacturers to stand out in the market by offering added value to their products.

The COSC certification is considered valuable for those who prioritize precision and reliability in their timepieces. The COSC, or the Contrôle Officiel Suisse des Chronomètres, is an independent Swiss organization that tests the accuracy and precision of watches. A watch that receives the COSC certification is designated as a chronometer, which means it has passed rigorous testing and meets high standards of accuracy.

The certification process involves testing the watch movement over 12 to 20 days, in different positions and temperatures, to ensure it maintains precise timekeeping. For many watch enthusiasts and collectors, a COSC-certified watch is a mark of quality and craftsmanship, often associated with higher-end timepieces.

The ISO 3159 standard is an international reference that governs methods for testing and evaluating the precision of chronometers. It seeks to establish uniform criteria for the testing and evaluation of timekeeping devices, whether they be watches, clocks or other chronometric instruments used in specific applications such as sports competitions, scientific instruments or military equipment. The ISO 3159 standard plays a key role in standardizing the methods used to ensure the precision, reliability and durability of chronometers.

Guarantor of precision: Users can have the assurance that chronometers tested in accordance with the ISO 3159 standard meet strict precision criteria, and that the results of the time measured are reliable.

Interchangeability: The uniform application of this standard throughout the world makes it possible for time measurement instruments to adapt to international measurement systems, offering greater flexibility for users.

  Performance optimization: By establishing clear criteria for chronometer performance, the standard encourages manufacturers to constantly improve the quality of their products.

  Certification and international recognition: Those chronometers that meet the requirements of ISO 3159 can be certified, enabling manufacturers to gain an international recognition for the precision and reliability of their products.

The ISO 3159 standard represents a major step forward in the management of chronometer accuracy and performance. By providing a framework for rigorous, standardized testing, it ensures that these instruments meet strict reliability criteria, which is essential in fields where time is critically measured. By ensuring greater reliability, this standard strengthens the confidence of users - whether industry professionals, top sportsmen and women, researchers or consumers - in the accuracy of the chronometers they use.

The COSC's role in the watchmaking industry is to certify the precision of Swiss watches by awarding them the designation of “chronometer.” This certification is a guarantor of high precision and quality, enabling manufacturers to stand out in the market. COSC carries out rigorous tests based on the ISO 3159 standard for mechanical watches and internal specifications for quartz watches. In addition to certification, the COSC offers testing services to help with the fine-tuning and industrialization of watches. It operates across three monitoring sites in French-speaking Switzerland, ensuring independence and neutrality in its controls.

The COSC's clients are companies that use its services to certify the precision of their watches. These companies may be watch manufacturers who wish to obtain the designation of “chronometer” for their products. COSC defines several terms for its clients:

-EXCELLENCE: The company using the COSC's services.

-Brand: Identification of the finished product marketed.

-Debtor: The company to whom the invoice is addressed.

-Depositor: The company that deposits the timepieces in the official COSC offices.

The series of watches submitted for certification must be accompanied by a deposit slip, which can be printed out via the COSC's secured portal.

For the COSC, being accredited by the Swiss Accreditation Service (SAS) means formal recognition of its technical and organizational competence as a calibration laboratory. This accreditation guarantees the quality, consistency and neutrality of the measurements carried out by the COSC. The COSC's independence as an association is a key factor in its rigor and credibility. The SAS, which reports to the State Secretariat for Economic Affairs (SECO), makes its accreditation decisions autonomously and independently, relying on technical expertise, suitable infrastructure and an impartial, well-managed organizational structure.

In order to know if a watch is COSC-certified, you can check whether it bears the designation of “chronometer.” This designation is awarded only to watches that have passed the COSC's rigorous precision tests. As a general rule, certified watches are accompanied by a chronometer certificate, although this is optional and depends on the watch brand. If you have any doubts, it is advisable to contact the watch manufacturer directly for information regarding certification.

The precision of a COSC-certified chronometer must be between -4 and +6 seconds per day. While this tolerance may seem high, it is in fact the result of extraordinary requirements. Even if a watch gained 6 seconds every day, it demonstrates remarkable regularity. Using the metric system for comparison, the error over a year's time would be equivalent to about 7cm for every 1000m. Mechanical watches, in particular, partially compensate for their deviations as a function of temperature and position, which is an essential quality of these high-quality watches.

In order to verify the precision of a watch, it is essential to follow several steps to assess its performance in relation to a time reference. Here are some commonly used methods:

-Use of a reference clock: Compare the time indicated by your watch with an atomic clock or a radio-controlled clock, which are extremely precise sources of time.

-Observation over several days: Note the time on your watch at a specific time each day and compare it with the reference time. Calculate the daily difference to determine if your watch is running early or lagging behind.

-Testing in different positions: Mechanical watches can vary in precision depending on their position (dial facing upwards, dial facing downwards, sideways). Test the watch in different positions to see if this affects its precision.

-Temperature monitoring: The precision of a watch can be affected by temperature. Try to check whether temperature variations affect the operation of your watch.

-Use of applications or measuring devices: There are applications and electronic devices that can help measure a watch's precision by recording the movement's beats and comparing them with a time reference.

These methods make it possible to determine the regularity and precision of a watch, ensuring that it operates within the tolerances acceptable for a certified chronometer, such as those defined by the COSC.

The COSC standard for automatic (mechanical) watches is based on the ISO 3159 standard, which defines the criteria for a balance spring oscillator wristwatch chronometer. To achieve the COSC certification, a mechanical watch must meet several stringent criteria over a testing period of 15 days. During this time, the watch is tested in five different positions and at three different temperatures (8°, 23°, and 38°C). The key criteria include:

• Average Daily Rate: The watch must maintain an average daily rate between -4 and +6 seconds per day.

• Mean Variation in Rates: The consistency of the rate over the testing period.

• Greatest Variation in Rates: The largest difference in rate observed during the tests.

• Difference Between Rates in Horizontal and Vertical Positions: Ensures the watch performs consistently regardless of its orientation.

• Largest Variation in Rates: The maximum deviation in rate observed.

• Variation in Rate Depending on Temperature: The watch's ability to maintain accuracy across different temperatures.

• Rate Resumption: The ability of the watch to return to its original rate after being subjected to different conditions.

Only watches that meet all these criteria are awarded the official chronometer certificate, signifying their high precision and reliability

A COSC-certified watch must have a precision that ranges between -4 and +6 seconds per day. This means that it can lose up to 4 seconds a day, but no more, in order to be considered a certified chronometer.

The accuracy of a COSC-certified chronometer is defined by specific criteria. For mechanical watches, the average daily rate must be between -4 and +6 seconds per day over the first 10 days of testing. This tolerance, while it may seem high, is actually indicative of a high level of precision. The testing process involves evaluating the watch in different positions and temperatures to ensure consistent performance. The certification is a testament to the watch's ability to maintain precise timekeeping under various conditions, reflecting the high standards of Swiss watchmaking

A chronometer is a high-precision timekeeping instrument, set to operate with great precision under various conditions of use. As defined by the International Organization for Standardization (ISO), a chronometer is certified by a neutral official body, such as the COSC in Switzerland, which carries out rigorous testing of the watch or movement and issues an official certification. Each chronometer is unique, identified by a number engraved on its movement and a certificate number issued by the COSC. It is important not to confuse a chronometer with a chronograph, which is an instrument designed to measure short time intervals and cannot be certified as a chronometer.

A chronograph is a timekeeping instrument with a counter for measuring and displaying time intervals irrespective of conservation or of telling the time. It might also include a recording device. Unlike a chronometer, a chronograph is designed to measure short times, such as the duration of a particular event. At present, there is no standard to certify the precision of a chronograph. However, high-precision watches that integrate a chronograph function can be certified as chronometers.

The main difference between a chronometer and a chronograph lies in their function and certification.

A chronometer is certified by a neutral official body, such as the COSC.

A chronograph is a timekeeping instrument with a counter for measuring and displaying time intervals irrespective of telling the time.

None. The COSC is the repository of analytical results that belong to its customers (the watchmaking brands). It does not have the authority to disclose information to anyone other than the legitimate owners of those results. The buyer should contact the head office of the brand to which the chronometer belongs.

No. Documents issued by the COSC are optional. It is for the brands themselves, and only them, to decide whether or not to communicate the results obtained during certification of the movement or watch by the COSC.

A COSC certificate is considered to be a valuable document. The COSC is authorized to issue only one single copy of a certificate, bearing the endorsement ‘duplicate’. In case of loss of a duplicate, the only way to obtain a new document is to subject the watch to new testing. In this case, only the brand may request this service. The head office of the brand that has marketed the chronometer must therefore be contacted directly.

Yes, a chronometer may be subject to as many tests as necessary, especially if the main components making up the movement have had to be replaced. However, only the brand may obtain this service.

The chronometer designation can be compared to a university degree. At a given moment in life, the candidate proved, on the basis of an examination, that they have met all of the performance criteria that allowed them to merit the designation. Just as is the case for a graduate, this designation is acquired for life, even if one's performance is likely to change somewhat over time.

The results for a chronometer are kept for 10 years, starting from the day of the end of testing. Beyond this period, no more information can be issued about a chronometer.