1795 - Breguet overcoil

The balance-spring is a small spring which regulates the oscillations of the balance. The flat balance spring, invented by Huygens in 1675, had established a degree of isochronism which still left something to be desired. The flat balance-spring was made of copper or iron, had only a few coils and was accurate as the pendulum of a clock.

In 1795 Abraham-Louis Breguet solved the problem by upraising the spring’s last coil and reducing its curvature, to ensure the concentric development of the balance-spring.

Source: breguet.com

Reported by: Władysław Meller

Other records: Timeline of Watchmaking Innovations