Power Reserve
How long the watch will run on a full wind before the mainspring runs out of energy.
What is Power Reserve?
Power reserve is the amount of time a fully wound mechanical watch will continue running before the mainspring exhausts its stored energy and the watch stops. It is sometimes shown on the watch face via a power reserve indicator complication, and is always listed in a movement's specifications.
Typical Ranges
Most mechanical watches have a power reserve of 38–48 hours, meaning a fully wound watch will run for roughly two days. Higher-end movements and modern designs often achieve 60–80 hours (convenient for taking the watch off over a weekend without it stopping). Some movements — particularly those designed for reliability at sea or in the field — achieve power reserves of several days.
What Affects Power Reserve
Several factors reduce effective power reserve:
- A worn or set mainspring — stores less energy than a fresh one
- Dirty or dry lubricants — increased friction throughout the gear train and escapement consumes more energy per tick
- Low amplitude — a sign that energy is being wasted somewhere in the train
After a full service with a replacement mainspring and fresh lubrication, most movements recover their full rated power reserve — often running noticeably longer than they did before the service.