... make a guess, what Patek this is ?
.... quite an interesting back case. I didnt know it can be detach from the main case....
It is ...
IMO it is a Ref. 3419, which can also be used as a pocket watch when the lugs are detached. kind regards erich
+1 On the concept...
Although I didn't know the reference number nor the watch itself; the concept of a wristwatch able to convert to a pocketwatch came to mind as well. I'm not 100% sure if Patek made a watch like this until mac_omega mentioned the Ref 3419.
... a real hardcore Patek collector !! YOU are correct !
Patek ref. 3419 with 12"'400 movement, 18 jewels....