A balance spring, also known as a hairspring, is a fine spring made of an alloy of iron and manganese that is used in mechanical watches as a regulating element. It is attached to the balance wheel and provides the restoring force that keeps the balance wheel oscillating back and forth. The balance spring is responsible for the accuracy of a mechanical watch, as its tension and shape determine how the balance wheel moves. The balance spring is responsible for maintaining the consistent amplitude of the balance wheel and therefore the watch’s accuracy.
