Glossary/Breguet Overcoil
Breguet Overcoil
A Breguet overcoil, sometimes called a Breguet spiral or spiral Breguet, is modification made to a hairspring in order to allow it to flex in and out from its center concentrically when the balance wheel is in motion.
By allowing the hairspring to store and release energy more concentrically, an overcoil helps to eliminate errors in the rate of timekeeping of a timepiece that are due to changes in its position.