How does it do this, you ask? The fusée is a cone-shaped object with helical grooves on its lateral surface (smaller cone at the top, and larger at the bottom). A fully wound spring will tug at the top of the cone. A less wound spring will eventually tug at the bottom. Thus, as the spring grows weaker, the “lever” grows longer.
Another series of rivets, levers, and blockers ensure that the fully wound and fully unwound state are blocked, thereby securing only that harmonious, constant middle. This is no easy task – the movement has 351 parts, and the chain has 636 with a cross section measuring in at 0.6 by 0.3 mm.
The only thing better than knowing these facts is witnessing them; and you can, because Lange has carved the three-quarter plate of untreated German silver to make these mechanisms visible. The rest is finished to standard Lange perfection, from a hand-engraved balance cock to a diamond endstone that functions as a bearing for the tourbillon.