Incidentally, this inspired me to look up information about the balance spring
of a watch. I found only one page, and that in Swedish, which gave the
information that the alloy Anibal was a steel alloy with 44.4% nickel.

This alloy was important because the bimetallic strips in a temperature-
compensating balance wheel then exhibited nonlinear behavior, so that they
compensated for the changes in elasticity of a plain steel balance spring or
hairspring in the middle of the range, not just at the ends of the temperature
range.

Think of how an apochromatic lens is superior to a normal achromat.

Of course, the Guillaume balance became obsolete as the same Guillaume invented
Elinvar, an alloy for the balance spring that had an invariant modulus of
elasticity.

John Savard