Thanks Andrew, and Mark for you very comprehensive reply!

Mark, with the production number, could you make an estimate of its birth year? I already have a feeling that it was fairly old as it has a wonderful even ivory colour patina ( stopper and subdial hands entirely, the hrs and minute hand as far as the lume is concerned) The dial is not pitch black but charcoalish. A beauty if I may say so. Great combination, dark charcoal with pale ivory.

So a mid sixties version maybe?

Ron