About Power Reserve Indicator Watches
A power reserve indicator represents the amount of tension that remains on a timepiece's mainspring. In automatic-winding watches, this then indicates the length of time the watch will operate while not being worn; in non-automatic watches, it shows the amount of operation time before winding the watch becomes imperative. The first prototype of such an indicator was devised in 1933 by Breguet, but it wasn't until Jaeger-LeCoultre's 1948 Powermatic series that the complication was available to the wristwatch community. Power reserve indicators are commonly needles or hands read against a zoned indicator, or a revolving wheel viewed through an aperture.