The Girard Perregaux 31.8 watch movement utilizes a pin-lever escapement and features a sophisticated excenter self-winding mechanism with just one gear stage. The excenter on the rotor arbor operates a lever, which in turn rotates a ratchet wheel through two clicks. On the dial side, a planet differential gear transmits the combined power from both automatic and manual winding to the barrel arbor via two planet wheels. This implementation allows for different gear ratios and ensures effective decoupling of the two winding sources. The movement is equipped with automatic winding, sweep second function, and was used during the period around 1978.