The term accuracy is often used in connection with watches. This gives an indication of the respective clock error, which is a deviation between the displayed time and the so-called time standard. Clocks that are very accurate are called time standards and are used to regulate others. Atomic clocks currently have the lowest error of rate and thus the highest accuracy of rate. However, such time deviations (clock errors) do not always have to be constant. They can also indicate variable deviations. If this error remains constant over a longer period of time, it is also called a steady-state error. In this case, the hands function properly, but a time is set that has a certain difference from the nominal time. The difference between the daily deviations is called a rate error. This can have various causes: On the one hand, it can be caused by external influences such as air pressure or temperature, and on the other hand, it can be caused by constant wearing. Particularly with mechanical watches, attempts are made to compensate for the rate accuracy. For these watches, care should be taken to ensure that the spring tension is always in the middle range. For this purpose, the watch should be wound regularly. Manufacturers also have the option of having their watches certified. This is done by the COSC (Contrôle Officiel Suisse des Chronomètres), which carries out 15-day tests to check the accuracy of the movement. This is the official testing centre for chronometers in Switzerland.
