Complex sentence: A balance spring, or hairspring, is a fine spiral or helical spring used in mechanical watches, marine chronometers, and other timekeeping mechanisms to control the rate of vibration of the balance wheel.
Split into simpler sentences: A balance spring, or hairspring, is a part used in mechanical timepieces. The balance spring is a fine spiral or helical spring used in mechanical watches, marine chronometers, and other timekeeping mechanisms to control the rate of vibration of the balance wheel.