My watch keeps running how ?  Yes it is a complicated feat to say the least and while every part of watch is critical to keeping accurate time, it would be difficult at best without the thin piece of metal that is the power source in mechanical watches.  That thin strip of metal that keeps curling and unwinding for what seems to be forever is actually and engineering wonder.  Imagine trying to design a strip of metal thin enough but yet elastic enough (not the best quality of any metal) to make sure your timepiece functions accurately all the time.  While it defies imagination in both its simplicity and complexity … there it is, taken for granted right on your wrist.  If you would like more information on the history, structure, and design of mainsprings, click on the following link:Mainsprings.