Omega Seamaster Professional 600.
This was the first generation of the watch that was to become known as PloProf. The case was machined out of one solid block of steel. Access to the movement is from the top after removing the bezel. I have included many pictures here so one can see all the parts involved with the movement removed as well. The red button is used to lock the bezel in desired setting. To change the setting one needs to push on the red button and turn the bezel. This watch was last serviced in 2008. The dial has a couple of imperfections, some paint chipped off in the center under the hands, can be seen more when the hands are removed. There is also a tiny blemish right under I in PROFESSIONAL as you can see in the pic. I think it is something the watchmaker somehow dropped there. May be it can be somehow removed but I did not want to try it and it can only be seen under magnification.