Power Reserve Indicator also called Réserve de Marche is a complication of the watch used to indicate the current energy level of the watch's drive unit. The power reserve indicates the instantaneous level of tension of the drive spring.
The power reserve indicator displayed on the watch with automatic winding movement shows how long a watch will function when not worn. On a manual winding watch, it shows the time left until the watch needs winding.
Power reserve indicators were employed very early on marine chronometers and later in the accurate Railroad grade pocket watches. The first wristwatch with the mechanism equipment with power reserve indicator was created by Breguet in 1933. However, this was only a prototype with only one watch assembled.
In 1948, Jaeger-LeCoultre introduced a power reserve indicator designed for production in a series of watches called the Powermatic which utilized the LeCoultre Caliber 481.
Notifier: Władysław Meller
Other records: Timeline of Watchmaking Innovations