Consummate Precision

Chronometers are considered as the most precise of mechanical timepieces. Their consummate rate accuracy gives them a special status. The term ‘chronometer’ on the face of a pocket watch indicated a special quality criterion even back in the 19th century. Only watches with the utmost accuracy could bear this quality label.

Longitude Act

However, the history of how the chronometer was invented goes back to the 18th century. Since there was no possibility on the high seas of navigating using time in reference to home time, the only way to steer a course was to use a sextant. It was John Harrison who first succeeded – as a result of the Longitude Act passed by the English parliament in 1714 – in determining longitudes that were essential for navigating reliably.

Pocket watches or ships’ clocks

If it was feasible to compare the local times at two geographical positions, the difference between them could then be calculated as a measure of longitude. This was the basis Harrison used to develop his legendary marine chronometers H1 to H4 as highly accurate timekeepers for sailing on the high seas. John Arnold undertook further improvements based on Harrison’s H4. He invented the term ‘chronometer’. Mechanical chronometers – in the form of pocket watches or ships’ clocks – remained essential for seafaring navigators right through into the 20th century. It was not until the advent of navigation using GPS that they were superseded.

In the 19th century, tests of chronometers were conducted at major observatories such as those in Paris, Greenwich, Liverpool, Hamburg and also Kew-Teddington.The test criteria were not always consistent.

The coveted “Class A” certificate

In 1910, a Rolex wristwatch was the first to be awarded official certification as a chronometer. The coveted “Class A” certificate was also awarded to another Rolex model by the famous Kew Observatory in Great Britain, which had been held in very high esteem as a certification body for marine chronometers since the 19th century. Back in the 1930s, Rolex already gave its own extremely accurate timepieces the designation “Officially Certified Chronometer”. In the late 1950s, this was specified in more detail: now the Datejust and Day-Date models bore the label “Superlative Chronometer Officially Certified”.

Superlativ Chronometer Zertifizierung

In 2015, this test procedure and consequently the certification were brought up to date. The Superlative Chronometer Certification is evident from the stringent rate tolerances: in contrast to those applied by the Official Swiss Chronometer Testing Institute for chronometers (COSC), they are set at an average daily rate of +2/-2 seconds. As if that were not enough, their inspection procedures also include tests for water resistance, magnetic field resistance, checking the power reserve and further extensive tests. Regular maintenance is essential so that a chronometer delivers all that it promises. Juwelier Wagner’s dedicated watchmakers’ workshop will devote their considerable skills and meticulous attention in servicing your timepiece.

COSC: Contrôle officiel suisse des chronomètres

Currently, the Official Swiss Chronometer Testing Institute, COSC for short (Contrôle officiel suisse des chronomètres), which was founded in 1973, is regarded as one of the most renowned independent certification centres. As the name indicates, it awards quality certificates based on a standardised test procedure in accordance with NIHS 95-11 / ISO 3159. This testing of a mechanical watch takes 15 days, during which the rate of the movement, which has not been inserted into the case, is calculated in five different positions at three temperatures. The average daily rate may not deviate from between -5 to +8 sec/day. If it can be proved that the movement complies with the COSC tests – chronograph movements are also examined in accordance with the given criteria – this is recorded in the technical details. This justifies the designation as a ‘chronometer’ on the watch face.

Premium-Segment

For example, Rolex has all movements undergo COSC certification – in addition to its own certification –, which entails additional costs but adds to the particular prestige of this brand of watches.

Admittedly, the renowned COSC does not have the same status as a Swiss government testing institute. This is what has led to several other watch manufacturers in the premium segment apart from Rolex also relying on their own certificates.

Zusätzliche qualitative Endkontrollen

Some watch companies, such as Jaeger-LeCoultre or IWC perform an additional final quality control not only for chronometers made in-house. The stringent “1000 Hours Control” test at Jaeger-LeCoultre as an internal series of tests for all models exceeds the official series of chronometer tests. It involves testing the movement before and after it is inserted into the case. The suitability tests and production controls include rate accuracy as well as testing temperature, pressure, shock, magnetic field and water resistance. Once all these tests have been completed successfully, you can be entirely sure that your chronometer is not only always the most accurate of timepieces but also extremely reliable.