Tony C.
··Ωf Jury memberWhatever the precise caliber, it's an Eterna, as the (big jewel) shock protection on the OP's example suggests.
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Very nice pickup! Birks Rideau were a line of dressier watches, many having Eterna movements. But I have a couple of chronographs with Vajoux movements, and at least one that maybe related to Breitling in some way. I also have an older Rideau with an A Schild movement.
If you tire of this one, let me know.