This watch is a “Prototype Seamaster 1000”. Omega used a “Seamaster 600” dial during the development of the “Seamaster 1000” possibly to keep secret the fact that the watch was rated to a further 400 meters of depth. The side of this watch is engraved: “Prototype 3-122”. The Prototype Seamaster 1000 differed from those produced commercially in its case back design. The prototype has a flat back while the commercially-produced watches have a slightly curved back. This watch is illustrated in Marco Richons book page 331.