Guillaume won the 1920 Nobel Prize in Physics for these discoveries, which shows how important these alloys were for scientific instruments.
Elinvar originally consisted of 52% iron, 36% nickel, and 12% chromium.
A major cause of inaccuracy in watches and clocks was that ordinary steels used in springs lost elasticity slightly as the temperature increased, so the balance wheel would oscillate more slowly back and forth, and the clock would lose time.
Chronometers and precision watches required complex temperature-compensated balance wheels for accurate timekeeping.
Springs made of Elinvar, and other low temperature coefficient alloys such as Nivarox that followed, were minimally affected by temperature, so they made the temperature-compensated balance wheel obsolete.