1930s Centre Seconds Sports Watch
I recently spotted the watch below for sale on a European sales site. It wasn't in the best of condition but I noticed it was the same watch as in a vintage advert I had a copy of.
Unfortunately the lume remaining in the hour hand was loose and fell out when I dismantled the watch for cleaning, so I had to relume both hands and repaint the red seconds hand.
The movement is a calibre 81-28 that has been adapted for centre seconds. I don't know if these movements had an official designation as they do not appear in any movement catalogues or other references.
And here is the restored watch with the advert from 1939. The serial number dates this watch to 1938. Helvetia seems to have specialised in sports type watches during the 1930s, highlighting their shock and waterproof qualities. See here for more information: 1930s Sports Watches, and 1930s Pilots' Watches.