The balance spring is arguably the single most critical component of a wristwatch. It’s responsible for making sure that the oscillations of the balance are consistent, but to do so, it has to address – both metallurgically and in its configuration – a number of challenges. Magnetism, temperature changes, and the fact that the balance spring needs to be shaped so as to expand and contract as perfectly concentrically as possible, are all issues with which watchmakers have grappled over the centuries. Innovations such as overcoil outer terminal curves (Breguet and Phillips), and the use of materials like, in the past, glass and even bamboo, and in the modern era, silicon, are all intended in one way or another to reduce the degree to which external influences interfere with with the balance spring.
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