The Accutron 2210

2210 front (dial side) view. 2210 back view.

Manufacturer: Bulova Watch Company Inc.
Dimensions: 19.4mm x 17.4mm x 4.0mm
Commencement of Manufacture: 1973
Tuning Fork Frequency: 440 Hz
Index Wheel: 270 teeth
Derived Calibres None


This, in my humble opinion, is the most interesting of all Bulova's tuning fork watches. It is the smallest tuning fork movement ever made, and it is a remarkable piece of design to fit the gear train into such a small space. It was mainly used in ladies watches. When used in men's watches, this little movement sat in a huge spacer ring, quite funny to see! The movement's low thickness of only 4.0 mm allowed for a very slim watch. Of course, as mentioned below, they had neither sweep seconds or date.

The tuning fork had to have curved tines to allow room in the center of the watch for the battery. (The example pic above has the wrong battery, as the original size is no longer available). The electronics had been reduced greatly in size as current technology allowed, in this case the coils were controlled by a hybrid integrated circuit. Another unique feature of this model is the initial reduction gear train. They had only a very limited amount of room, and so they used worm gears on the first two reductions to achieve the required ratios. In fact, the little worm gear train is in an area that is 4mm x 3.5mm x 2mm. The train reduction in this little "gearbox" is 840:1. At the top of the vertical worm gear, you can see the index wheel edge-on. This little area is in the bottom right corner of the right-hand pic above. Some more work will be done to work out all the gear ratios from the index wheel to the hands, as there are some strange numbers here to be found ie. a 270 tooth index wheel running at 440Hz gives the index wheel a speed of 1.629629629 etc Revs per second, then divided that by 840:1, followed by some further reductions. When is get 5 mins to spare, Ill go thru the whole train.

Another interesting feature, at least from the service point of view, is the the coils could be replaced without dismantling the movement. This was also possible in the 230 series. If the crown is pulled out, as for setting, the watch consumes only 1/3 normal power, so it can be stored like this. It was never offered with a sweep second hand, or date, as the mechanical arrangement would not allow for easy adaption to this. This is an interesting one to own if you are a musician, as the fork is tuned to exactly A=440Hz, standard concert pitch. I wonder if this was deliberate. (Just a thought - I think it was coincidence!).