Omega

lever movement, 20 jewels, mono-metallic balance, blue dial, luminescent baton indexes, large orange minute hand, aperture for date, oversized asymmetric case with raised reeded revolving bezel calibrated for 60 minutes, large red button for releasing bezel, screw-down crown with protective lock, hooded lugs, case back with anti-slip grooves, case, dial and movement signed, with a stainless steel Omega 'shark'  bracelet and clasp

This model, the Omega Professional Seamaster 600, was taken into production in 1970 and was originally designed for use by deep-sea divers and became known as the 'PloProf,' for 'Plongeur Professionel.'

To prevent the popping of the crystal when decompressing the watch after diving, Omega created the vacuum case which does not allow air to penetrate the case. It is made out of one piece of massive steel and fitted with an especially strong crystal and a protected crown.

When diving, one can calculate how much oxygen remains in the tank and adjust the bezel for accurate timing. By pushing the red button, the locked bezel releases and the bezel can then be adjusted.

The excellent overall condition of the present watch makes it exceptionally collectible.

The 'PloProf' is described and illustrated in Richon, M., 'Omega Saga', pp.136-137.