Resonance improves a mechanical watch's accuracy by coupling two balance wheels so they synchronize and mutually correct for disturbances, gaining rate stability that a single oscillator cannot achieve. Two contemporary manufactures have made this centuries-old phenomenon work in a wristwatch, and they do it in fundamentally different ways: F.P. Journe lets vibrational energy travel indirectly through the shared mainplate, while Armin Strom connects the balances directly with a patented steel clutch spring. The distinction matters, because it determines how precisely the balances must be regulated before resonance can begin at all.
The Physics of Resonance: Enhancing Precision
Resonance, as Joshua Munchow explained in a detailed technical essay for Quill & Pad, is "a phenomenon in which a vibrating system or external force drives another system to oscillate with greater amplitude at specific frequencies." In a watch, the vibrating systems are two balance-and-hairspring assemblies. When they are tuned nearly identically and coupled closely enough, each begins to influence the other through tiny, almost imperceptible vibrations that are transmitted, received and mutually shared between them.
The chronometric payoff is twofold. As Frank Geelen described on Monochrome, the benefit can be improved timekeeping, chronometric consistency, or both — consistency meaning the watch can be expected to gain or lose precisely the same number of seconds every day. Armin Strom adds that two balances regulating each other in real time can counteract the negative influence of wrist motion, gravity, temperature changes and shocks, yielding oscillation-rate stability and torque compensation.
Writing for SJX Watches, David Ichim identified a more specific mechanism: better resistance to positional errors. If small defects — a heavy bias on a balance wheel, uneven breathing of a hairspring — appear in both oscillators and they beat in a locked anti-phase mode, the errors have a good chance of canceling each other out. The coupling becomes useless during shocks, but it is of great use against the positional errors caused by gravity.
