Is your watch running too fast or too slow?
What determines the rate of a mechanical watch?
In this image, the expansion and contraction of the hairspring are visible as the wheel turns. The outer end of the hair spring is fixed to the arm, the balance cock, that holds the upper pivot of the balance wheel. The inner end of the hairspring's coils are fixed to the balance wheel axis.
Mechanical watches do not have perfectly steady rates. The rates are changing throughout the day as a watch runs. If everything else is functioning well, the intent of the regulator is to evenly distribute rate errors over longer periods of time, error created by things like the watches physical orientation throughout the day, or temperature changes, so that on average the watch reads well over this period of time, such as a whole day. But it is a relatively fine adjustment.
What if a watch runs very, very fast? Like gaining a minute or more in an hour?
A hairspring problem is the most common cause of a watch running very much too fast. A watch with such trouble can be as much as 15 minutes fast in an hour. There are other causes too. For example a mainspring that is too strong can drive the escapement too fast. The escapement may be damaged causing it to sometimes slip. Or a wheel may be missing a tooth causing it to jump ahead as the bad spot comes around.