Introduction
COSC is a unique organisation that plays a significant part in the validation of the precision and subsequent quality of chronometric Swiss watches.
The existing organisation of COSC was established in 1973, its head quarters are based in La Chaux-de-Fonds. The Swiss Official Chronometer Control (COSC) is a non-profit association, working for the Swiss watchmaking industry. It was created by five cantons Bern, Geneva, Neuchâtel, Solothurn, Vaud, along with the Federation of the Swiss Watch Industry (F. H.).
Prior to 1973 more labs existed but independently. They were brought together by the 5 cantons to create a unified independent bench mark that would service the Swiss industry.
A COSC technician feeding a series of movements through the optical measuring system, that checking the rates by the physical location of the seconds hands.
definition of a Chronometer
The Swiss Federation of Watch-Manufacturers' Associations (F. H.) describes the chronometer as a watch that has obtained an official rating-certificate. For examples; CHRONOMETER
Unique certificates
COSC's official laboratories (OL) inspect over 1.8 million instruments - mechanical and quartz yearly.
Each certified chronometer is unique. Each mechanism is identified by a serial number engraved on its movement with an associated certificate number issued by COSC.
Image of a certificateHistorical figures
200,000 certificates were issued 1976
Over 2 million certificates have been issued in each of the passed two years.
"Approximately 6% of Swiss watches exported carry COSC." (F. H.)
To view the annually published reports from COSC https://www.cosc.swiss/en/cosc/key-figures. These figures are not representative of the total number of Swiss watches produced only the 6% that carry a COSC certification.
Standard TESTS
There are four categories of timepiece that can qualify for COSC, 1. mechanical wristwatches with an oscillating balance and balance spring, 2. pocket watches, with an oscillating balance and balance spring, 3. clocks, 4. quartz wristwatches.
The 3 labs that carry out the tests on the movements are located in Saint-Imier, Le Locle and Bienne operate 7 days a week, approximately 350 days each year. In 2019, 681,843 certificates were issued in Saint-Imier, 737,405 in Le Locle and 812,637 in Bienne.
All 3 labs are designed identically, using the same design of workshops and storage areas, equipment, techniques and logistics, all centralised and viewed from the main office in La Chaux des Fonds. If one of the labs was to be closed for any reason, one or both of the alternative locations, could theoretically absorb all of the required tests on the movements from the closed lab.
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The chronometric certification of a wristwatch with balance spring is based on 7 elements required by the ISO 3159 standard.
Tests are made over 15 days. The movement is checked using two key pieces of data, 1. The temperature and 2. The physical position of the watch (3 o’clock, 6 o’clock, 9 o’clock, dial-up, dial-down). These two elements fundamentally can affect time-keeping. The tests do not include forms of simulation equivalent to a watch being worn by an end consumer.
The movements are fixed on trays each holding five pieces. The trays are then moved into the 5 different positions inside controlled thermal enclosures for 24 hours and tested at 3 different temperatures (8°, 23° and 38°C). Daily the movements are removed for a short period of time from the enclosures to take the necessary measurements, using optical control machines equipped with 5 cameras in a row one for each movement being tested. The daily measurements made by COSC on each movement determine the rates/status of each one in relation to a set period.
This approach (shown in images further down this page) is used for volumes of the same calibre. For individual movements COSC executes the same approach of tests but in a specialised work-station tailored to individual and small numbers of pieces.
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Non-standard testing
A service COSC is little known for is their non-standard tests. Recently a client requested calibres to be tested consistently at much lower temperatures than usual for COSC certification, for a product that was to experience severe conditions on a polar expedition. The first round of tests found that the calibres failed due to the lubrication effecting precision at sub-zero temperatures. The client was able to alter the types of lubrication to ensure the final tests were successful. These forms of tests do not carry certification but allows Swiss brands to test products under specific alternative conditions to validate specialised products.
The Procedure
On day -0- when the movement is received, COSC performs the following procedure.
The numbers engraved on the movement that are associated to the final certificate correlate to the documentation supplied by the client are verified.
One of the work stations that checks that the numbers are correctly associated from the movement to the tagging on the outer container and entered into the system.
An image from one of the monitors verifying the engraved serial number of the movement with the tag applied to the container it is housed in during the tests.
The engraved serial number being validated and cross referenced is in the lower part of the green square.
The movements are received from the manufacturer in the boxes to the right.
The operator then takes each one, scanning and cross-referencing the movements details through the camera linked to the validation and entry software, that is set into the centre of the desk with the red light.
After validation, the movements are transferred into new trays (to the left) specifically made for the movements size, then to be tested.
The movement being viewed by the camera linked to the system.
The movements are placed in 5-slot trays, in series.
The movements (delivered unwound) are wound according to the brands instructions.
One of the machines used to wind the movements. The working winding-crowns on the movement stems correlate in diameter to the 5 collets that hold them in order to be wound.
A tray of 5 movements being wound simultaneously the correct number of turns of the winding stem to fully wind the movements, whether automatic or manual in origin.
If the movements are automatic winding, the automatic system is either removed or disengaged to be wound up uniquely via the winding stem. This protects the automatic mechanisms from potentially being worn out or damaged as the movements are being wound manually by the winding crown.
The movements are then placed in an enclosure at 23°C (± 1°C), where they remain for at least 12 hours to stabilise their temperature before the tests begin.
The 23°C enclosure. Prior to entering there is a secondary connecting room that is also permanently closed to assure the temperatures remain as consistent as possible. The 23°C enclosure is the first in the series of temperature controlled rooms, due to the extended time, compared to the other temperatures, the tests are carried out for.
The trays are placed in specific places and in different positions within the enclosure.
During the tests the boxes of trays are turned into different positions. All of the boxes are numbered to avoid confusion and the orientation is shown by the labels attached to each set. Those in the image above, are placed in the 12 o’clock down position.
The first section granting access to the 23°C enclosure, beyond this is the 38°C and 8°C enclosures.
The doors to each section can not be opened until the connecting doors are closed. In addition the 38 and 8°C enclosure doors can not be opened simultaneously.
The optical measurements being taken.
The trays of movements to be tested are received from the right hand side of the operator.
Each platter of 4 sets of trays, containing 5 movements is then placed onto a central automated shelf.
The shelf then automatically moves backwards aligning the first row of 5 movements with the optical measuring equipment. Each camera measures the initial position, or eventual de-placement position of the seconds hand, and the information is stored on the IT system
The shelf quickly moves forwards as each row of movements are viewed and the seconds hands recorded by the row of 5 cameras creating the red light shown.
For 15 days for wristwatches and pocket watches, 19 days for clocks, 13 days for quartz timekeeping instruments – there are daily tests. Every day, including weekends, the time-pieces are measured and wound. This requires the teams of technicians to work on a shift basis to ensure all time-slots are covered. On the basis of the measurements, 7 elimination criteria are calculated for Type I, mechanical wristwatches, shown in the grid below.
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Below are the limits associated to the testing of mechanical watches. (For quartz watches and clock the details can be found on www.cosc.swiss)
The daily rate is the difference between two periods in time, separated by 24 hours.
Keys to the 7 criterior
Avg R: the average of the daily rates of the first 10 days of testing.
Avg V: the average five absolute values of variations obtained for the five positions during the first 10 days of testing.
Max V: the value of the largest of the five rate variations, relative to the vertical three positions of the watch during the first 10 days of testing.
D: the difference between the vertical and horizontal rates of the watch, obtained by subtracting the average rate of the 9th and 10th days of testing from the average rate of the first two days of tests.
P: the absolute value of the largest of the differences between the first 10 rates and the average daily rate of the tests.
C: the variation of the rate as a function of temperature, obtained by subtracting from the rate at 8°C from that at 38°C, the whole divided by the temperature interval between these two rates.
R: the variation between the last rate of the tests and the average of the first two rates of the tests.
Category 1 movements with a diameter larger than 20 mm or where the surface area is greater than 314 mm2. Category 2 includes all movements with a diameter of 20 mm or less, and a surface area not exceeding 314 mm2.
The certificate implies that all the instruments entrusted to COSC operators for testing, are tested by a neutral and independent body.
A Unique System
The Official Laboratories, are the soul labs in the world to apply this standard industrially, issuing well in excess of 2,000,000 official chronometer certificates per year.
An attestation of COSC certificate issued BY Breitling
Some of the requested criteria details posed to a client regarding the instrument to be tested by COSC, for a movement with balance-spring oscillator.
Manufacturer of the movement
Manufacturer's reference
Associated calibre reference
Does the movement include a chronograph mechanism
Frequency (Hz)
Maximum arming torque (mNm -Newton-metre, “moment of force”)
Minimum arming torque (mNm- newton metre, “moment of force”)
Diameter of the movement
Height of the movement
Position of the winding crown in relation to the 12H position on the dial.
Manual winding or Automatic
Winding direction of the winding crown
SAS accreditation
For twenty years COSC has been accredited as a calibration laboratory with the Swiss Accreditation Service, SAS. This accreditation guarantees the quality, consistency and neutrality of the controls made. The independence of COSC is a primary factor to its credibility.
The SAS answers to the State Secretariat for Economic Affairs (SECO). It's actively involved in the organisation of the Conformity Assessment Bodies (CABs), in accordance with international standards.
The accreditations it grants signify the formal recognition of the technical and organisational competence of an organisation to perform a defined service within the scope of the accreditation.
Competencies
The SAS relies on the following competencies in issuing its accreditations:
Staff: technical skills, practical experience in the technical field concerned, continuing education.
Technical infrastructure: decision-making criteria, premises and equipment, procedures.
Organisational structure: independence, impartiality, quality management.
COSC since….
As mentioned earlier, the premises that house the three testing laboratories in Le Locle, Saint-Imier, and Bienne are all new, developed from 1973. They are equipped with an infrastructure complying to the environmental conditions required by the ISO standards.
The testing equipment, developed and produced by COSC, is constantly updated to adapt to the progress made in the watchmaking world.
The Laboratories
To ensure the reliability of its tests, COSC has equipped its premises with various systems including the following:
The floor is covered with a copper grid, to prevent staff from being charged with static electricity that could affect the instruments being tested.
An airlock to filter out dust and a controlled environment to ensure the levels of temperature and humidity, in the thermal chambers and measuring laboratory.
COSC IT portal, provides all of the brands the ability to connect to it, using their own security code. Each has a personalised access, that enables them to link directly with COSC.
Atomic Clocks
Each Lab uses a time based on two atomic clocks and a synchronised DCF77 0CX0 clock, it makes use of two different time references (GPS and DCF). The data entry and calculation are fully computerised.
(DCF77 is a longwave time signal broadcast station at Mainflingen, Germany, 25 km south-east of Frankfurt. The DCF77 radio signals are derived from an atomic clock, and broadcasted on 77.5 kHz.)
The screen is linked to the IT system and monitors time, temperatures and humidity. There are sensors through out the building ensuring constant checks on the stability of the environment.
The readings from the 3 clocks shown on the monitor taken from the two atomic clocks and a synchronised DCF77 0CX0 clock.
Permanent monitoring
The air is continuously monitored by probes in all thermal chambers and the laboratory. Temperature, humidity, and dust, are also subjected to constant monitoring. The results of this monitoring are stored in the IT system and allow COSC to answer any query from an applicant regarding environmental conditions.
Rigour and confidentiality
The management team at La Chaux-de-Fonds maintains IT control of all data concerning the arrival of the series, packaging, environmental conditions, possible alarms, measurements, and the final results. This applies to all three Laboratories.
Diverse tests
The skills and equipment used in chronometric certification activities can also be made available to the Swiss watch industry for any type of tests related to the rate of timekeeping instruments.
COSC is able to carry out multiple rate tests on the timekeeping instruments entrusted to it. These tests do not necessarily lead to the title of chronometer, but they can facilitate or even accelerate the development and industrialisation of watches as discussed in Non-Standard COSC Tests at the beginning of this page.
FAQ’s posed to COSC.
Is every chronometer sold with a certificate from COSC ?
No Documents issued by COSC are optional. It is for 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.
What if a COSC certificate has been lost ?
A COSC certificate is considered be a valuable document. COSC is authorised to issue only one copy of a certificate, bearing the word ‘duplicate’. In case of loss of a duplicate, the only way to obtain a new document is to subject the watch to a new control. In this event, only the brand may request this service. The head office of the brand that has marketed the chronometer must therefore be contacted directly.
What to do if a COSC certificate has been damaged ?
The damaged certificate must be returned to the brand that marketed the chronometer. The brand alone may obtain a new original certificate (without duplicate) by returning this document to COSC.
Can a chronometer be certified several times during its lifetime ?
Yes, a chronometer can be subjected to as many checks as necessary, especially if major components of the movement have had to be exchanged. However, only the brand can obtain this service.
How long is the chronometer certification valid ?
The chronometer label can be compared to a university degree. At one point in its life, the candidate has proved on the basis of an examination that it has met the performance criteria that allowed them to bear the label. As for a graduate, this title is acquired for life, even if their performance is liable to change somewhat over time.
How long does COSC retain the results of its measurements ?
The results for a chronometer are available during 10 years, from the day of the end of the tests. Beyond this period, no more information can be issued about a chronometer.
In the basement of each lab is the same set up of systems ensuring air-filtration, temperature and humidity. Every section is checked manually daily as well as being connected to the IT system with a system of alarms if the variations exceed COSC requirements.
To learn more about COSC