Fusee (horology)

A fusee (from the French fusée, wire wound around a spindle) is a cone-shaped pulley with a helical groove around it, wound with a cord or chain attached to the mainspring barrel of antique mechanical watches and clocks. It was used from the 15th century to the early 20th century to improve timekeeping by equalizing the uneven pull of the mainspring as it ran down. Gawaine Baillie stated of the fusee, "Perhaps no problem in mechanics has ever been solved so simply and so perfectly."[1]

Mainspring barrel and fusee
A fusee in a 1760 pocket watch by Johan Lindquist of Stockholm
  1. ^ Cite error: The named reference White1966 was invoked but never defined (see the help page).