It was produced from 1953 to 1960, and during that period it was divided into four generations.
The first generation had a three-piece case with a bezel that extended to the edge of the case. The second generation changed to a two-piece case, which increased the thickness and volume. In the third generation, the hour markers on the dial were changed from a type that was punched and applied to holes to a type that was glued on, and in the fourth generation, the Cal.12-600AT was changed to a Cal.27-460.