AUTONOMY

The autonomy of an instrument, and of a watch in particular, is the length of time during which it can operate without any new supply of energy — neither winding of the spring, nor changing nor recharging the battery. For a mechanical watch, this length of time depends on the amount of energy stored in the Mainspring and on the consumption of the Movement; it is more commonly referred to, in the vocabulary of the Horologist (watchmaker), by the term Power reserve. Modern watches offer autonomies ranging from around forty hours to several days, or even several weeks for calibers with multiple barrels. For a watch with Quartz, Autonomy corresponds to the battery life, which varies from two to several years. Autonomy is an important practical criterion: a sufficient reserve avoids untimely stoppages and repeated resetting of the time. It results from a compromise between the size of the spring, the efficiency of the Train (wheel train) and the Frequency of the oscillator.

Historically, knowing the charge state of the Barrel was already a major concern: marine chronometers carried a Gauge indicating the time remaining before they needed to be wound. On wristwatches, the Display of the Power reserve became widespread in the 20th century.