Isochronism is the attitude of a resonator to maintain the same frequency at different amplitudes. The English term “isochronism” is regularly engraved on the bridge of certain movements. It is the real grail of almost all watchmakers for centuries.

This isochronism applies to any resonator, whether it is a wall clock with a pendulum, a pocket watch or a wristwatch with a balance wheel and a balance spring as resonators, or an electronic watch that used to have a tuning fork as a resonator, or nowadays, for the most part, a quartz.

Whatever the amplitude of the resonator the period of the oscillation must remain the same, this is the objective of isochronism. The isochronism can be negatively affected by equilibrium defects, by magnetism, by escapement or other factors.