How to Differentiate Between a Chronometer and a Chronograph

A chronometer is often mistaken for a chronograph. By learning their similarities and differences, you can tell a chronometer from a chronograph instantly

Two of the most common terminologies in watchmaking and yet are often confused for one another are the chronometer and the chronograph. For the newly initiated who look to delve deeper into their budding passion for watches, understanding the difference between a chronometer and a chronograph is essential to the journey.

In today’s strict horological terms, a chronometer defines the precision expected of a timepiece. To be called a chronometer, the movement of a timepiece must possess certain qualities pertaining to its accuracy, reliability and consistency before it can be certified as such. The chronometer certification is under the purview of the Contrôle Officiel Suisse des Chronomètres (COSC). One of the important criteria to “Certified Chronometer” is that the movement mustn’t deviate from -4 and +6 seconds per day. A chronometer could be of any watch type, for example, diving, racing or aviation.

This modern definition of chronometer is a significant departure from the original, maritime-related form, known as the marine chronometer, invented during the Age of Discovery. Nevertheless, the word chronometer originates from Greek. It is an amalgamation of two words: chronos (time) and meter (measure), and as a whole, translating to “time measurer”.

Back when modern innovations such as satellites and the GPS hadn’t yet been created, seafaring explorers navigated the world using celestial clues, based on the appearance of the sun, moon, stars and planets in the sky, to help determine their current positions in the open ocean. While celestial navigation was reasonably accurate, other factors such as the knowledge and skills of the navigator bore an influence on such accuracy. The need to ascertain a mariner’s precise location at sea led to the development of a portable precision timepiece called the maritime chronometer that could be installed aboard a ship. This instrument shouldn’t be confused with the chronometer certification, which is the topic of this article.

Founded in 1973 at the initiative of Swiss watch brands, the COSC is an independent, non-profit institution responsible for the chronometer certification today.

While competitive chronometry and the original chronometer certification predated the COSC, with the founding of the COSC, the chronometer standard was tightened significantly in order to elevate the precision and prestige of Swiss Made watches. Currently, the COSC operates three state-of-the-art laboratories in Bienne, Le Locle and Saint-Imier, and it certifies over 2 million movements and watches each year, including mechanical wristwatches, pocket watches, fixed-time devices and quartz wristwatches.

To obtain the “Certified Chronometer” certification, mechanical movements must meet the criteria set out in ISO 3159. They are subject to comprehensive and rigorous testing over the course of 15 days of multi-stage testing in a variety of positions (3 o’clock, 6 o’clock, 9 o’clock, dial on top, dial on the bottom) and temperatures (8 °C, 23 °C and 38 °C) to simulate real-life conditions.

Back when modern innovations such as satellites and the GPS hadn’t yet been created, seafaring explorers navigated the world using celestial clues, based on the appearance of the sun, moon, stars and planets in the sky, to help determine their current positions in the open ocean. While celestial navigation was reasonably accurate, other factors such as the knowledge and skills of the navigator bore an influence on such accuracy. The need to ascertain a mariner’s precise location at sea led to the development of a portable precision timepiece called the maritime chronometer that could be installed aboard a ship. This instrument shouldn’t be confused with the chronometer certification, which is the topic of this article.

Founded in 1973 at the initiative of Swiss watch brands, the COSC is an independent, non-profit institution responsible for the chronometer certification today.

While competitive chronometry and the original chronometer certification predated the COSC, with the founding of the COSC, the chronometer standard was tightened significantly in order to elevate the precision and prestige of Swiss Made watches. Currently, the COSC operates three state-of-the-art laboratories in Bienne, Le Locle and Saint-Imier, and it certifies over 2 million movements and watches each year, including mechanical wristwatches, pocket watches, fixed-time devices and quartz wristwatches.

A fine example of a chronometer is the Bell & Ross BR-X5 collection bearing movements produced by Kenissi, certified by the COSC as chronometers, where timekeeping precision is guaranteed to be within -4/+6 seconds per day.

Recently, there have been reports attributed to the COSC director Andreas Wyss that the institution is looking to reduce the accuracy requirement for COSC-certified movements to less than 10 seconds per day. In other words, a chronometer would become even more precise in the future.

The chronograph is among the most useful complications and most common watch types. The word originates from Greek, loosely translating to “time writer”. Indeed in the early days, the instrument was created to time events. Louis Moinet invented the chronograph in 1816 to track astronomical objects. Another pioneer, Nicolas Mathieu Rieussec was entrusted by King Louis XVIII, known for his passion for horse racing, to create the first marketable chronograph in 1821. The modern chronograph is used chiefly to track elapsed time.

The chronometer certification provides an unequivocal assurance to collectors that the movement of the chronometer has been tested independently and can be relied upon to operate within the set standard. One can expect a chronometer to be an exceptional watch.

Luxury watches are products of in-house expertise, years of development, flawless execution and uncompromising scrutiny. In fact, some watch brands have gone a step further to subject their watches to even stricter internal standards and intense examinations. As such, these watches rightfully carry dual certifications.