<iframe src="https://www.googletagmanager.com/ns.html?id=GTM-52DKJGF" height="0" width="0" style="display:none;visibility:hidden">
See latest articles

What is a Chronometer?

Often misunderstood or confused with a chronograph, a chronometer is fundamentally a highly accurate mechanical watch movement that has undergone – and passed – strict precision tests over a period of time in a host of different circumstances.

Chronometer testing measures the movement of the watch towards a set of accuracy standards, in different positions and at different temperatures.

Watch brands use a neutral, independent organization to conduct the individual testing. Since precision tests are so intense, only a small percentage of watches on the market today are certified chronometers. A watch must pass through intense testing in order to carry the term “Chronometer” on its dial.

Now that you understand the basis of a chronometer certification, let’s take a look at how chronometers have evolved into the modern certification.

History of Chronometers

The chronometer was first developed in the 18th century after decades of research and development. At the time, during the 1600’s and 1700’s, seafaring exploration was in full swing, and many ships would run aground and perish because they couldn’t determine longitude, as there was not an accurate clock aboard the vessels to do the calculations. In 1707, in a single incident at sea, more than 2,000 sailors died when their homebound British ships ran aground on jagged rocks.  As a result, in 1714, the British government issued a contest, called the Longitude Act, with a hefty monetary prize that would equal several million today, to encourage watchmakers and scientists to develop a “precise and useful” way to determine longitude on the high seas.

The first working marine chronometer was invented and built by British watchmaker John Harrison, working with different materials to render friction-free parts that were impervious to rust. It then also took him years to convince the Longitude Board that his clocks worked. After multiple sea-faring journeys, it was determined that the clock built was indeed accurate at sea. Finally, with that precise working clock operating at a fixed location (Greenwich Mean Time), sailors could make some quick calculations at local noon and determine the ship’s longitude. Not only did this save lives and ships, but also enabled countries to build their naval and exploration powers.

Later in the 1880s, Longines became involved in high-precision timekeeping and produced its first movement for a certified chronometer, the 21.59 calibre. This chronometer movement is based on a calibre developed in 1878 which was adapted to improve its accuracy. 

L2.821.4.11.6 Longines Record watch
L2.821.4.11.6 case back Longines Record watch

Chronometer Wristwatch Testing

Over the centuries, as clocks evolved and wristwatches came into being, the concept of conquering the feat of chronometer status for the wrist remained important.  Today, a wristwatch can achieve chronometer status if the movement inside it has been certified according to strict standards by an outside observatory.

There are chronometer testing facilities in Besancon, France, in the Saxony region of Germany,  in Japan and other places around the world, including several in Switzerland.  Chronometer criteria can vary slightly from each observatory. For Swiss watches, the most well-known and prestigious observatory is the Controle Officiel Suisse des Chronometers (COSC), with three locations in Switzerland. When collectors refer to their watches as being “COSC certified”, it means the chronometer certification comes from the Controle Officiel Suisse des Chronometers.

Focusing on the standards of the COSC, certification criteria is based on ISO 3159 standards. To gain chronometer certification from COSC, it is tested for 15 days in five different positions and in multiple circumstances such as extreme temperatures, humidity, pressure and more. Measurements are taken daily and are compared with two independent atomic clocks.

During testing, watches are placed in various positions: 3 o’clock, 6 o’clock, 9 o’clock, dial on top, dial on the bottom. Each watch remains in each position and given temperature for 24 hours. Each day, the watches are removed for a brief moment to take measurements.

Only watches that meet the precision criteria can be granted an official chronometer certificate. The mechanical watch may not have a daily variation of more than -4 or +6 seconds per day. Only approximately 3% of watches produced in Switzerland will make their way through COSC’s certification process. The chronometer certification ensures that each individual mechanical watch tested is durable and incredibly precise.

When watch brands utilize a chronometer movement inside a watch, most will indicate “chronometer” stamped on the dial. After all, they have conquered a lot to achieve this status.

“To gain chronometer certification from COSC, it is tested for 15 days in five different positions and in multiple circumstances such as extreme temperatures, humidity, pressure and more.”

Longines Chronometers

More often, chronometers will include other innovations within the movement to increase their efficiency and precision. Longines, for instance, builds its chronometer movements with silicon balance-springs that have great longevity. The balance-spring is the watch’s regulating organ that oscillates around its position of equilibrium, thereby exercising its fundamental role: to maintain a regular rhythm. By using a silicon balance-spring, the material is resistant to normal temperature variations, magnetic fields, and atmospheric pressure.

Longines currently has two collections in its lineup wherein all of the watches are certified chronometers. Those collections include the Record Collection and the Longines Spirit. The watches are all sold with a chronometer certification card attesting to their ultimate precision, and have a 5-year warranty.