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Glossary of watchmaking

Balance spring

Spiral | ヒゲゼンマイ | 摆轮游丝

Balance spring

A very fine spring and the "heart" of a mechanical watch. Its ends are affixed to the balance and the balance-cock. Its elasticity allows the balance to make regular oscillations. Its length, and the balance's moment of inertia, determine the duration of each oscillation. Its length can be altered to regulate the watch.