Power Reserve Watches

The power reserve indicator is one of the most useful features of a mechanical watch besides the actual time display. A mechanical watch is operated either by automatic or manual winding. In order to run at a regular rate a mechanical timepiece needs to have at least 30 per cent of its mainspring wound. An automatic timepiece needs to be worn for about 10–15 hours before it is fully wound. 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.

History

There are numerous devices for recording the amount of mainspring power stored in the barrel. Power reserve indicators were employed very early on marine chronometers and later in the accurate Railroad grade pocket watches. Today they are used in wrist watches. The first wristwatch with the mechanism 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. Thus, Jaeger-LeCoultre was ostensibly the first watchmaking company to launch wristwatches with a power reserve indicator.