In watches , the power reserve designates the time that the mechanism of a mechanical watch can continue to operate without it being raised or carried, for automatic watches . The term applies only to watches drawing their energy from the tension of a spring as opposed to those operating with a battery.
Most of the mechanisms have a power reserve of about 40 hours. Others, more complex, display several days of autonomy. Finally, some watches have a complication , ie a small dial that indicates the power reserve in the manner of a fuel gauge or power.
When the power reserve is exhausted, the mechanism stops. It is then necessary to reassemble the watch and put it back on time. To avoid an automatic watch does not stop when it is not worn and the need to adjust, small boxes called rotary turntable watches simulate the movements of the wrist to keep watch Operating.