Display complication
What is a power reserve indicator?
A small gauge on the dial that shows how much energy is left in the mainspring before the watch stops.
How it works
A mechanical watch runs on a coiled mainspring that unwinds over its power reserve, often 40 to 80 hours. A power reserve indicator uses a differential gear between the winding side and the running side of the mainspring barrel to show how wound the spring is.
It's most useful on hand-wound watches, so you know when to wind, and on watches with long reserves, so you know whether it will last the weekend off the wrist.
History
Marine chronometers used power reserve indicators, called up-and-down indicators, so navigators never let them stop. Wristwatch versions became popular in the 1940s and 50s, and the German name, Gangreserve, appears on many Glashütte watches.
Before you buy
Power reserve indicators are inexpensive on Japanese automatics and common on German and Swiss watches. Check the movement's total reserve too: a long reserve matters more than the gauge.
Power reserve indicator watches we've measured
- Nomos Glashütte Metro Date Power Reserve 1101
37 mm case · 43.6 mm lug-to-lug · $4,420
Questions
- How long is a typical power reserve?
- Most automatics run 38 to 50 hours when fully wound; newer movements reach 70 to 80 hours, and some exceed five days.