The Fusée And Chain: From Function To Fashion In 4 Wristwatches From A. Lange

The fusée is a cone-shaped component connected to the mainspring's barrel by a chain As the mainspring is wound, the rotating barrel winds the chain around the narrowing fusée As the watch runs and the power stored by the mainspring decreases, the tension from the fusée's chain on the barrel, now rotating in the reverse direction, ensures that a consistent amount of energy is released through the movement until there is none left.

While the chain and fusée served a functional purpose in the past, it quickly became impractical following the emergence of new metal alloys for mainsprings and balances In 1994, A Lange & Söhne introduced the first wristwatch ever outfitted with a fusée and chain system: the Tourbillon Pour le Mérite.

Once A Lange & Söhne had successfully incorporated a fusée and chain into a wristwatch, other manufacturers soon followed Now examine the Zenith Academy Georges Favre-Jacot, a wristwatch oscillating at 5 Hertz with a chain and fusée added to the mix. Source