A little video showing how the Cal 321 emerged and how the base movement was used by others including Patek.
Still flying the urban legend that the 321 was modified from the cal 2310. I ask anyone to step forward to tell me what was supposedly done to modify it! Other than the engraving on the bridges stating 321 and Omega of course..... Hint: Lemania supplied the 2310 with the same guilt plates so it's not that. And Lemania was operating independently, at one point the owners of Heuer, for more than a decade before Breguet was resurrected. More of that if you read Jack Heuer's and the late Nicolas Hayek's autobiographies .
The 27 Chro was also the basis for the worlds first automatic chronograph. More than 20 years predating the competitors. Also designed by the same Albert Piguet, but stopped by the Omega directors as they saw no use for it.
...Not to mention one of my favorite threads on this forum: https://omegaforums.net/threads/omega-chronograph-movements-over-the-years.26518/