Power Reserve
The length of time a mechanical watch can last without being rewound is indicated by the power reserve. Tension from the spring is used to power a watch, once this tension dissipates the watch must be rewound to return this tension for the watch to continue operating.
The power reserve lasts about forty-eight hours on standard models.
More sophisticated models may use a gauge on the dial and are able to continue to run for several days without the need for rewinding.
Petite SonneriePVD