to my (small) knowledge, all the first issued 50FF had this inverted "30"... Like in the ad below (except that all the "30"inverted have a triangle and not a diamond shape bezel) π...
According to the owner, and the former owner, this one was used by the French Marine Nationale. I knew they existed, but this is the first one I see in person. You will notice the triangle at twelve, And the early case number 6xx. When watches have both c...