Tuning fork is a type of watch movement that keeps time with a small vibrating tuning fork instead of a balance wheel. A transistor circuit keeps the fork vibrating. The Royal Museums Greenwich describes Bulova’s Accutron, built this way, as the earliest electronic watch. The design came before the quartz watch.
How does a tuning fork watch work?
A mechanical watch uses a mainspring, hairspring and balance. A tuning fork watch replaces them with a transistor circuit and a small fork. The circuit keeps the fork vibrating. In the Bulova Accutron, the fork vibrates 360 times each second. That vibration turns an index wheel, and the index wheel drives the hands. In Calibre 214, the index wheel has 300 teeth. The high rate of vibration let the Accutron keep time to within about two seconds a day.
Where it comes from
Swiss engineer Max Hetzel developed the idea after he joined Bulova in 1950. The result was Calibre 214, the first tuning fork movement sold commercially. It was introduced in 1960, and sales began in 1961. Every Bulova Accutron movement ran its fork at 360 Hz. Ebauches SA in Switzerland later made its own family of tuning fork movements, called Mosaba, from 1968 to 1976. These ran at 300 Hz. Omega also made watches with tuning fork movements.
How is it different from a quartz watch?
Both a tuning fork watch and a quartz watch keep time with a vibrating resonator. Neither relies on the balance wheel of a mechanical watch. In a tuning fork watch, the resonator is a small fork, kept moving by a transistor circuit. The tuning fork watch came first. It is also easy to tell apart from a mechanical watch by ear. It does not tick. The vibrating fork gives off a faint, high-pitched hum instead.
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