There are plenty of resources around here on the web on the oddballs that are tuning fork watches. Long story short, before quartz happened during the late 70s, the tuning fork was the most accurate of watch movements.
The most famous tuning fork watches brand is probably Bulova, with their Accutron models. The 214 was their first tuning fork caliber, then came the 218 and several spinoffs (2210, 230, 219).
If there’s one defining characteristic of the tuning fork watches, it probably is the sweeping hand. The tuning fork oscillates at 360 Hz1, and every oscillation makes the index wheel move forward. As a result, the whole movement turns with 1/360th of second increments. To the eye it appears as a continuous sweep, of course.
The Accutron was the ancestor to several other tuning fork watches, in two noticeable very different ways : first, it was copied by the Soviet and the Chinese. The copies are the Slava Transistor and the Tian Jin tuning fork watch. These two are close replicas of the 214 caliber.
The legitimate offspring of the Accutron is the “Mosaba” caliber. This was manufactured by ESA for several brands, from Omega (their f300 models) to Tisssot, Zenith, Logines or Certina, among others.
- On most models ; the 2210, for instance, hums at 440Hz which makes it a valuable gadget for musicians (as 440Hz is the concert “A”). ↩︎