The Zenith bumpers (133, 133.8 and 71) were creations of Ephrem Jobin, the same man that designed the observatory competition monster the cal. 135 (
http://omegaforums.net/threads/who-was-ephrem-jobin.2807/). They are excellent movements, but a developmental dead end, as Zenith switched to Martel's rotor automatics as soon as it acquired that firm in 1960.
The 133 differs from the 133.8 in the beat rate. The 133 runs at 18,000bph and the 133.8 at 21,600bph. THere are a few other differences in detail but they are fundamentally the same movement.
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