There have been various speculations in the past whether the Unitas/Eta 6497 calibers had some sort of connection to, or were even derived from the old Cortebert movements used by Rolex for vintage Panerai watches. The position of the wheels and jewels is very similar, but since this applied to many other calibers as well, the connection was never conclusively confirmed.
However, there is indeed one caliber from Cortebert which appears to be the missing link between the Cortebert Cal. 616/618 and the early Unitas 285/497 (predecessor of the Unitas 6497).
It is the Cortebert Cal.727, a hybrid of Cortebert 616 and Unitas 285/497 with a diameter of 16,5 Linge (36.6 mm). 16,5 Ligne is a size that was typically used by Unitas. The size of the Cortebert Cal. 616/618 and Cal. 620/622 is 16 Ligne whereas the Cal. 624/626 has a diameter of 17 Ligne.
Pocket watches were not popular anymore in the 1960s. It appears that, in order to save costs, Cortebert ceased the production of large pocket watch movements and started using the Unitas 285/497 instead. Initially with their own classic bridge design and later with standard Unitas specs.
This caliber has the very same technical configuration and dimensions like the Unitas 285/497 units. It also shares the very same main plate. The only difference is the design of the bridges, which obviously follows a similar style that was used by Cortebert for many decades. An interesting detail is the Cort stamp on the main plate. It is unknown if this caliber was produced by Cortebert itself or by Unitas on specific request of Cortebert.
The dial side of the Cal. 727 movement is identical with early Unitas 285/497 calibers. The setting lever jumper (3) has the same outer shape but the Cortebert version has an opening in the center.
Unitas 285 and 497 share the same main plate and they only differ in the shape of the bridges. Cal. 497 already has the typical bridge shape that is in production until today.
There is another Cortebert caliber that has the same technical configuration with an Unitas unit. It is the Cortebert Cal. 726/736. This caliber has a size of 18,5 Ligne (41 mm) and corresponds with the Unitas Cal. 6431/6445.
The following chart illustrates the transition from the old Cortebert movements to the modern Unitas units that were used by Officine Panerai SpA in 1993 for their Pre-Vendôme watches and after 1997 also by Richemont.
At some point, Cortebert ceased the production of large pocket watch movements and started using common Unitas 6497 units with “Cortebert” engravings. This happend probably due to the rationalizations that occured within the Ébauches SA group, a holding of which Cortebert and Unitas were members since many decades.
Cortebert disappeared in the mid 1970s as one of many Swiss watch manufacturers who became victims of the “Quartz crisis”.
The OP XI/Eta 6497-2 caliber that was produced for Richemont Panerai has bridges that were redesigned in an attempt to achieve a similar look as the historical movements.
Are you interested in the historical movements that were installed in vintage Panerai watches? Here is the complete list.
Thanks for your interest.
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It´s a real pity that Cortébert which was akin to good movements didn’t survive the onslaught of the quartz movements and Japanese watches. I own one that belonged to my father. It is a CAL 451 bumper automatic movement. It needs adjustment as it runs fast 5 minutes per day. Still I wear it every day. it came inside a case #8535 which I would love to find one in unused state! Thanks for your research its so good to read!