It should be added in conclusion that power reserve problems often have very long time constants, sometimes measured in weeks, making the problem exceedingly hard to pinpoint. That is, a fully wound watch falling victim to one of the problems discussed above may lose just a small part of its power reserve in 24 hours. As a result, it may take weeks before the watch stops for the first time. An unfortunate consequence is that the direct cause-effect relationship is obscured as the watch owner searches for some recent event to explain the mysterious stoppage of the watch. For the above problems, a winder is the obvious solution.
Winders are now available in a very wide variety of types and price ranges.
Until now, we have been discussing the energy interchange process between the rotor and the mainspring, the kinetic energy of the rotor being transformed into the potential energy stored in the mainspring's spiral. Well, there comes a point in a mainspring's power curve when it can no longer store up any energy. It becomes fully wound, in our terminology. So it keeps on trying to put more and more energy into the mainspring. Unlike the case of the mainspring in a manually wound watch, the outer end of an automatic watch is not rigidly connected to the inner wall of the mainspring barrel.