The rugged Oyster case was great to match demands in certain specific professional fields. We all know models like the Submariner (intended for Divers), GMT (intended for Pilots), Daytona (intended for racing) etc. but it actually started in the early 50’s with the ‘Turn-O-graph.’ The name basically meant that the bezel could turn so it could be used for measurements (‘graph’). Its very first model (ref. 6202) looked design-wise like what was later going to be the Submariner. Very rare and sought after reference.