Skip to content
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

The bimetallic balance has a rim of two fused metals — brass outside, steel inside — cut at two points. As temperature rises, the brass expands more and curls the free rim arms inward, compensating the weakening of the steel hairspring. It made the marine chronometer and precision pocket watch possible and dominated fine watchmaking until nickel-steel (Invar-type) hairsprings with self-compensating alloys displaced it in the 20th century.

In the object catalogue

Catalogued objects whose own source record mentions “Bimetallic balance”. The quoted line shows where; it is the seller’s or museum’s wording, not independent verification.