Adri
·Unmarked vs marked crowns. Possibly. I thought that too, but the average watch maker wouldn't have zenith crowns. If the watches were sent to zenith for service then I think the crown would have been left unmarked.
I am thinking of doing a bit of research into the large and small case back marking to see what variations that throws up?
To help, if anyone has a mk 1 could they post the crown type and case back symbol size please?
For me small Zenith sign on the case back and unmarked crown.