In watchmaking, power is not a fixed value: it is a curve. The mainspring delivers maximum torque when fully wound and minimum torque when nearly depleted, and this variation is the central problem every movement designer seeks to solve. The mainspring itself — a spiral in non-magnetic alloy like Nivaflex, composed of cobalt, nickel, and chromium to resist metal fatigue — is the source of all the movement's energy. But being a good source does not mean delivering power evenly.
The gear train transfers this energy from the spring to the balance wheel through a sequence of teeth wheels with progressively decreasing diameter. Every junction is a point where power is lost to friction or transmitted irregularly. Larger wheels, like those chosen by Vianney Halter in his La Resonance, have higher tooth counts and allow smoother transmission. It is a clean mechanical solution, without patents or electronics.
The historical solutions to the problem of irregular torque are four: the stackfreed, the fusée-and-chain, the remontoire, and the constant-force escapement. The fusée is the most elegant geometrically. A chain connects the barrel to a cone: when the spring is wound and produces maximum force, the chain runs on the narrow side of the cone, reducing leverage; as torque drops, the chain moves toward the wider base, increasing leverage. The two effects compensate each other. Ferdinand Berthoud still uses it today in the FB1. The remontoire works differently: it rewinds a small auxiliary spring at regular intervals — every ten seconds in the Lederer 9012 — so the balance wheel always receives the same impulse, regardless of the main barrel's state.
The modern approach passes through stop-work. The classical Geneva system discards the first and last turns of the barrel, where torque is most irregular. Armin Strom developed a version adapted for automatic movements — the Declutch stop-work — which lets the spring slip through the unused turns instead of locking it, guaranteeing uniform power from start until the end of power reserve. Series barrels, as in the MeisterSinger MSA01 caliber, distribute the load across two tanks that charge simultaneously, flattening the overall torque curve.
The platinum micro-rotor in Patek Philippe's 31-260 caliber addresses the problem from another angle: it does not equalize the delivery but increases charging efficiency by 20% compared to the previous generation, reducing time spent in low-tension zones. The same efficiency principle guides Seiko's Magic Lever, introduced in 1959, which reduces losses during automatic rotor rotation. From the bench, what I still see today is that most series watches work with a usable torque band that is about 60% of the stated power reserve. The rest is declared margin, not real margin.