The more comprehensive Chronometer Certification

Observatoire Chronométrique+

The new ‘Observatoire Chronométrique+’ (OC+) certification certifies that a watch complies with the requirements drawn up by independent Swiss horology laboratory TIMELAB and authorises it to bear the prestigious and official title of “chronometer watch” in accordance with the internationally recognised ISO/CEI 3159 standard. The guarantee covers the finished watch and extends to other aspects relating to its reliability such as water resistance (ISO 22810), magnetic resistance (ISO 764), power reserve and performance on the wrist, in conditions representative of modern life. Each test and its individual requirements is described in detail below. Every individual Venturist is tested in Geneva for 21 days and is only awarded the ‘Observatoire Chronométrique+’ certificate if all tests are 100% successful.

Water Resistance

To ensure a watch is water resistant according to the ISO 22810 standard each watch has to withstand 3 different tests.

First (1) the ‘air overpressure test’. The watch is placed inside a device and exposed to differential air pressure. The watch shall show no air-flow exceeding 50 μg/min. Then (2) follows the ‘water overpressure test’. During this test the watch is placed inside a full water tank simulating an immersion at the defined depth.

To confirm the water resistance of the watch a condensation (cold water drop) test is done where the watch is placed on a heated plate at a temperature of 45 °C until the watch reaches the temperature of the heated plate. Then a cold drop of water is placed on the glass of the watch. After 1 minute, the glass is wiped dry. If condensation appears on the interior surface of the glass, the watch fails the test. The last test (3) is the ‘water resistance into low depth’. The watch is placed inside a water tank at a depth of 10 cm for a fixed duration of 60 min. Then, to confirm water resistance, a new condensation test is applied and again no condensation should appear inside the watch to pass the test.


During the chronometer test each watch head is individually tested for 17 consecutive days, in 5 different positions, at 3 different temperatures (8°C, 23°C and 38°C). Measurements are made daily with the aid of cameras and must be compliant with the ISO 3159 standard which allow insignificant daily rate deviations, within an average daily rate value from -4 to +6 sec (99,99% accuracy).

Based on these measurements, seven eliminatory criteria are calculated, each of which must be met; (1) average daily rate, (2) average variation of rate, (3) the greatest variation of rate, (4) the difference in rate between the watch’s horizontal and vertical positions, (5) the greatest difference in rate, (6) the precision of the rate in the event of temperature variations and (7) rate recovery.

To complete the test, a wearing simulation is performed which takes an additional 2 days.


When wearing a watch it is exposed to different magnetic fields on a daily basis. Smartphones, computers, tablets (and even their cases) but also speakers, microwaves and the well-known airport metal detectors all generate magnetic fields around them. Depending of the exposure level watches can be disrupted or even shut down.

The magnetic resistance test is performed by applying a magnetic field of 4800 A/m to the watch in 3 different positions. After applying the magnetic field the accuracy is measured to register the impact of the magnetic field. Then the watch is demagnetised and a new measurement is performed. Both measurements have to fall within the criteria specified in the ISO 764 standard.

Power Reserve

To test the power reserve, the watch is fully wound and placed into a device that is specifically designed to measure the power reserve of mechanical watch movements. Once the watch is out of power the measured power reserve is compared to the expected power reserve.

If the measured power reserve meets or exceeds the expected power reserve, the watch passes the power reserve test.

In-depth video about the OC+ certification and its tests

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