エルジン
The Elgin National Watch Company and the Hamilton Watch Company pioneered the first electric watch The first electric movements used a battery as a power source to oscillate the balance wheel. During the 1950s Elgin developed the model 725 while Hamilton released two models: the first, the Hamilton 500, released on 3 January 1957, was produced into 1959. This model had problems with the contact wires misaligning, and the watches returned to Hamilton for alignment. The Hamilton 505, an improvement on the 500, proved more reliable: the contact wires were removed and a non-adjustable contact on the balance assembly delivered the power to the balance wheel. Similar designs from many other watch companies followed. Another type of electric watch was developed that used a tuning-fork resonator instead of a traditional balance wheel to increase timekeeping accuracy, moving from 2.5–5 Hz with a traditional balance wheel to 360 Hz with the tuning-fork design.