A power reserve is the amount of time a mechanical watch can run after it has been wound. If a watch is stopping too soon, a simple home test gives you useful information before service.
Start with a full wind
Check the manual first. For a hand-wound watch, wind slowly until you feel firm resistance, then stop. For an automatic, give it the recommended number of crown turns. Many take roughly 30 to 40 turns, but movements vary.
Record the start
Set the watch to a known time, place it in a safe resting position, and write down the exact start time. Do not keep wearing it during the test because wrist movement adds energy.
Let it run
Check periodically and record when it stops. The difference between the start and stop times is the observed reserve.
Interpret the result
A small difference from the advertised figure may be normal. A much shorter reserve, especially with poor timekeeping, can point to incomplete winding, movement wear, dried lubrication, or a mainspring problem.
Repeat the test once before drawing conclusions. If the result stays low, have the movement inspected.
Learn more in our guide to watch power reserve.