Horology glossaryDefined term / hairspring
Hairspring
The fine coiled spring that oscillates with the balance wheel, governing a mechanical watch's rate and accuracy.
Authentication note
Why this detail matters.
A hairspring's material and geometry are specific to a caliber, and some manufacturers use proprietary hairspring alloys or shapes that are difficult to replicate. A movement with the wrong hairspring type for its claimed caliber, or visible evidence of amateur regulation, is a technical detail an authenticator examining the movement checks for.