Power Reserve Indicator
A display showing approximately how much stored running time remains in a mechanical watch.
Also known as: Power-reserve indicator, Reserve de marche, State-of-wind indicator
Definition
A power reserve indicator shows how much running time remains in a mechanical watch before the mainspring can no longer power the movement. The display is mechanically linked to the state of wind and may use a hand over an arc, a rotating disc or another indication. It is distinct from power reserve itself, which is the duration the movement can run from a full wind.
Why it matters
It is especially useful on manual-wind watches and long-reserve movements because it tells the owner when winding is actually needed rather than relying on memory.