A chronometer is a high-precision timekeeping instrument that has been tested and certified to meet specific standards of accuracy and reliability. In the realm of watchmaking, a chronometer is a watch that has undergone rigorous testing by an official certification body, such as the Contrôle Officiel Suisse des Chronomètres (COSC) in Switzerland. These tests assess the watch's performance under various conditions, including temperature fluctuations and different positions, to ensure it maintains precise timekeeping.

Chronometers are distinguished by their exceptional accuracy, often deviating by only a few seconds per day. This level of precision is achieved through meticulous craftsmanship and the use of high-quality materials and components. The certification process involves a series of tests conducted over several days, during which the watch must demonstrate consistent performance within the stringent parameters set by the certifying authority.

In horology, the term "chronometer" signifies not only technical excellence but also a mark of prestige and reliability. Watches that earn the chronometer designation are highly sought after by collectors and enthusiasts who value precision and craftsmanship. The certification is often indicated on the watch dial or case, serving as a testament to the timepiece's superior quality and performance.