What is a chronometer-certified watch?

　　What exactly is a chronometer-certified watch? Let us take a look below.

　　Contrôle Officiel Suisse des Chronomètres (known by the French abbreviation COSC). The COSC is an independent association governed by the Swiss Civil Code.

　　Watchmakers hope that their best models can earn this title, so they send their movements to the COSC. The COSC tests the movements with their cases open, and closes them up after the testing is complete. The chronometer testing institute issues a performance certification for every watch that successfully passes the test.

　　There are three official testing centres in Switzerland, located in Geneva, Biel and Le Locle, where manufacturers can send their watches for testing.

　　Switzerland began officially testing chronometers in 1878, while the Swiss testing institute we see today was established in 1973.

　　4. What tests are carried out?

　　The testing institute uses cameras and computers to analyse data during complex precision tests on movements. There are 7 types of tests in total. Failing to meet the minimum standard in any of the tests results in rejection. Testing is highly complex, and the following is merely an attempt at a simple summary.

　　Test 1:

　　Mean daily rate: After 10 days of testing, the mean daily rate of the movement must remain within a range of minus 4 seconds to plus 6 seconds per day. The institute determines the mean daily rate by subtracting the time indicated by the movement 24 hours earlier from the current time.

　　Test 2:

　　Mean daily variation: The testing institute observes the movement rate in 5 different positions (two horizontal positions, 3 vertical positions) once a day for 10 days, yielding a total of 50 rates. The mean daily variation must not exceed two seconds.

　　Test 3:

　　Maximum daily variation: Among the 5 daily variations across the 5 positions, the maximum variation must not exceed 5 seconds per day.

　　Test 4:

　　Difference between horizontal and vertical rates: The testing institute subtracts the average rate in the vertical positions (days one and two) from the average rate in the horizontal positions (days nine and ten). This difference must fall within minus 6 seconds and plus 8 seconds.

　　Test 5:

　　Greatest variation in rate: The difference between the maximum daily rate and the mean test rate must not exceed 10 seconds per day.

　　Test 6:

　　Variation in rate due to temperature: The testing institute tests the movement rate at 8 degrees Celsius (46 degrees Fahrenheit) and 38 degrees Celsius (100 degrees Fahrenheit). It subtracts the rate at the higher temperature from the rate at the lower temperature and divides the result by 30. The variation must not exceed 0.6 seconds per day.

　　Test 7:

　　Resumption of rate: This is calculated by subtracting the average of the mean daily rates of the first two test days from the mean daily rate of the final test day. The resumption rate must not exceed 5 seconds. Simple, isn't it? If a movement meets all these standards, the testing institute awards it a chronometer certificate.

　　5. How many movements does the testing institute test each year, and how many certificates are issued?

　　In 1995, the Swiss Official Chronometer Testing Institute tested 844,043 movements. This was a slight decrease compared to the record high of 883,714 movements tested in 1994. Most of the submitted movements passed the test. In 1995, the Swiss Official Chronometer Testing Institute issued a total of 814,868 certifications, accounting for 96.5% of the total applications. This means that chronometers accounted for 2% of the total production of finished Swiss watches.

　　6. Why are the majority of chronometers mechanical watches?

　　Quartz movements accounted for only one in three hundred of all movements submitted for testing in 1995 (totalling 3026). This is because electronic quartz technology is inherently defined as an ultra-precise form of timekeeping, making it less necessary to prove the precision of a quartz watch. This differs from the situation with mechanical watches. Even so, the testing institute has established extremely rigorous regulations, and quartz watches cannot be called chronometers until they pass these tests. Notably, the leader in Swiss quartz chronometers remains Krieger Watch Corporation of Miami Beach, Florida, which accounted for two-thirds of all certificates issued in 1995.

　　7. Do many companies apply for chronometer certificates for their watches?

　　In 1995, more than 60 companies submitted applications to the testing institute.

　　8. What is the demand like for chronometers?

　　Despite a drop in applications in 1995, watch companies experienced a surge in chronometer applications over the past 10 years. Swiss observatory data shows that movement submissions hit a low in 1976 before bouncing back to 225,712. Application figures did not surpass 1984,300 until 000. They remained on a steady upward trajectory throughout the late 80s, and by the 90s—driven by the powerful influence of Rolex alongside the sweeping revival of Swiss mechanical watches on the global market—applications rose rapidly. In 1990, the number of movements submitted to the Swiss observatory and successfully passing tests exceeded 600,000 for the first time. By 1994, the figure reached 883,714, marking an increase of 43.5% compared to 1990.

　　9. Which company is the leader in producing Swiss chronometers?

　　Rolex is the undisputed king of chronometers. Surprisingly, in 1995, 83% of all certifications issued by the Swiss observatory were awarded to Rolex (exceeding 675,000 pieces). When you realise that only 5 companies (one of which is a group) produce more than 6000 chronometers annually, you gain a real sense of Rolex's dominance in this field. The second largest producer is TAG Heuer (51,638 pieces, 1995), followed by Omega (31,135 pieces), Cartier Group (6393 pieces) and Bulgari (6056 pieces).

　　10. What is the difference between a chronometer and a chronograph?

　　These two terms sound very similar, but they have absolutely no connection to one another. As we have seen, a chronometer is a super-precise timekeeper, whereas a chronograph is a watch featuring a stopwatch function.

　　11. So what is a marine chronometer?

　　A marine chronometer is used on ocean-going vessels to determine longitude by measuring time. It emerged in the 18th century.