Power reserve indicator
Template:File left A power reserve indicator indicates the state of winding of the mainspring barrel.
Overview
Power reserve indicators (known as "Réserve de Marche" in French) were developed alongside long power reserve movements which can run for more than 2 days. Typically shown on the dial with a pointer, power reserve indicators are also sometimes located on the movement itself, visible through a display caseback or aperture. They are often geared directly to the winding system and usually use a gearing mechanism based on estimated power for a given number of winding turns. Others are attached to the barrel and use mainspring torque as an indicator of power reserve remaining.
Some power reserve indicators are marked with a fixed number of days, while others show a simple "+/-" or "ab/auf" ("up/down" in German). There can also be power reserve indicators for further functions, for example the alarm function.
History
Breguet developed a prototype power reserve indicator in 1933 but did not bring it to production. Jaeger-LeCoultre introduced the modern power reserve indicator in 1948 on the Powerwind Ref. 163 watch's Cal. 481. Jaeger-LeCoultre heavily marketed this feature in the Futurematic watches of the 1950s and continues to offer a model bearing the name, Réserve de Marche today. Zodiac was another early company to use a power reserve indicator, introducing it in 1949 on a pioneering automatic watch movement.