Accutron

The American company, Bulova produced an innovative line of timepieces during the 1960s and 1970s: the Accutron.

Bulova's headquarters are in New York, USA; however, all Accutron watches were made in Switzerland (1).

Two of the most noticeable characteristics of the original Accutron are the extremely smooth sweep of the second hand and the hum of the tuning fork.

At the time, the tuning fork driven mechanisms of the Accutron were the most accurate consumer timepieces available, accurate to within two seconds per day. The improvement in accuracy was largely due to the increased frequencies used by the Accutron movements - anywhere from 300 Hertz, ranging upto 720Hz in the movements licensed to Omega watches; most of the Bulova movements vibrate at 360Hz.

In comparison, the movement of a traditional balance wheel watch oscillates at 4Hz.

Any disturbance to a traditional mechanical movement has a larger impact because of the relatively slow oscillation. Traditional movements are more susceptible to changes in the consistency and quality of internal lubrication and friction surfaces. On top of that, the performance of traditional movements are more dramatically affected by the effects of gravity and temperature compared to the Accutron's tuning fork movement.

Later versions of the Accutron used quartz to regulate the electronics of the watch. In some models, the tuning fork was still present, but served no part in the regulation of the circuit. Eventually, the tuning fork was removed altogether.
Modern-day Accutrons are now largely indistinguishable from any other quartz watch.

Tuning fork Accutrons only need maintenance every decade, opposed to every 5 years for other mechanical timepieces. Finding spare parts for Accutrons is difficult, particularly the delicate ruby index wheels and coil assemblies. If you have a working Accutron, treat it well.

Updated: 1st November 2003, added more detail.

References:
(1) http://www.bulova.com/about/faq.aspx:
Q: Is Bulova a European company?
A: No. It is an American Company. It was founded in New York City in 1875. Some of our products, however, do come from other countries. For example, all Accutron watches are Swiss made.

Other information largely from:
The Accutron Watch Page: http://members.iinet.net.au/~fotoplot/acc.htm

Bulova is in fact a Swiss watchmaker. They invented the Accutron system in the 30's but it was impossible up to the late 60's to miniaturize it enough to make a usual size watch out of it.

Accutron watches are truly fascinating pieces of technology, because they use a variable magnetic field to keep a diapason vibrating at 60hz (120hz in later models). They have a transistor, a capacitor and other electronic components in, and they were built in the 60's! The vibration of the diapason is enough to have a small stepper moving, and this makes a wheel turn, and so you have a working watch.

Accutron watches were the most accurate watches that you could have in the 60's, so were used on aircrafts and even by astronauts. They also built a beautiful Accutron Spacewiev model, all made from glass so that you could see the insides. And this was 25 years before Swatch came about with the same idea!

Yes, I do own a Spacewiev, did you notice it?