Think of the main spring as the battery, and the balance wheel as a kind of resistor. The balance wheel is manually tuned to oscillate at a specific rate, relea

Think of the main spring as the battery, and the balance wheel as a kind of resistor. The balance wheel is manually tuned to oscillate at a specific rate, releasing the stored energy one little beat at a time. You are right that a mechanical system like that isn't perfect. You will get a kick out of a thing called a "Tourbillon" if you look that up - it was an attempt to improve the accuracy of mechanical movements by having the entire movement rotate as it unwound, in the hope of mitigating the effect of gravity on the accuracy of the watch over the course of the day.