We live in a world of instant gratification and when it comes to watches that is so true. I love to be able to take a quick glance at my mechanical or automatic watch and know how much energy is left to keep my timepiece running.
Power Reserve Indicator (originally called Réserve de Marche) is a complication of the watch, which is designed to show the amount of remaining stored energy. The power reserve indicator indicates the tension on the mainspring at any particular moment.
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 an 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.