Cal. 221 was the smallest Bulova Accutron movement, and the smallest tuning fork movement ever produced. Introduced in 1973 at the Basel Fair, Cal. 221 was intended for ladies watches. It measured just 19.4 mm by 17.4 mm and was 4.0 mm thick.
Due to its small size, some unusual engineering choices were made. Like the earlier compact Cal. 230, the tuning fork operates at 440 Hz, but the reduction gears are quite different. A tiny gearbox includes a worm gear and stacked reduction gears from a 270 toothed index wheel. Unlike the flat disc-shaped coil of Cal. 230, this movement returns to a cupped coil as on the original Accutron movements. Because the battery is so large in comparison to the movement, the tuning fork curves around it on both sides.
Just one version of Cal. 221 was produced. According to the usual Accutron naming convention for movements with no seconds hand or calendar complication, it was called Cal. 2210.
Bulova Ladies Accutron Movements
Unlike the earlier well-known Accutron movements, which ran at 360 Hz, the ladies models operated at 440 Hz. They used a 270 tooth index wheel to turn the wheel train, though Cal. 221 lacked a seconds hand entirely.
The so-called “Mini-Accutron” debuted at the Basel Fair in 1970. Cal. 230 was quite advanced, with miniaturized electronic components. The electronic coils were radically different, being placed on a disc-shaped element between the tuning fork ends rather than on “cups” around the ends. The movement measured 8.75 ligne (19.4 mm) in diameter and was 5.2 mm thick.
Cal. 230 was further enhanced in 1973 with a larger 10.5 ligne (23.50 mm) version for men’s watches. This was achieved with a larger main plate, but all of the components remain the same.
Also in 1973, Bulova added Cal. 221, the smallest tuning fork movement ever made. Measuring just 19.4 mm by 17.4 mm and 4.0 mm thick, this movement required special engineering. The tuning fork is curved to wrap around the battery, and a worm gear driving stacked reduction wheels in a tiny gearbox.