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The Encyclopedia of Horology

Glossary · Regulation

Bimetallic balance

A split balance rim of two metals that changes shape with temperature to compensate the hairspring.

Explanation

Brass on the outside and steel within: as temperature rises the rim arms curve inward, reducing the moment of inertia to offset the weakening of a steel hairspring. Compensation balances were superseded by alloys such as Invar and Elinvar, which made a monometallic balance viable.