I recently bought what I thought was a Rolex case with a mismatched movement and dial, but I am starting to have second thoughts. The dial is marked "Tisdall" and "waterproof." The movement is marked "Crest." In my research, I couldn't find much on Tisdall, but I did find that Gruen made a movement called Crest. From my research in the Rolex bible, I found that Gruen had a relationship with Rolex concerning the Rolex "Prince." Is there a chance that this possible Gruen movement is correct in this Oyster Watch Co. case? Sorry for the low res photos...these are the ones I dragged off the ebay listing after the auction finished.

Here is a shot of the movement.

This is the underside of the back cover.

I think I have managed to identify the movement from doing a search in the 1950 Paulson's Master Key Swiss Catalog. It seems to be a 10.5 ligne Cyma (Tavannes) movement as shown on page 102 (Paulson's Cyma 162, 163). I don't think there was a relationship between the Oyster Watch Company and Cyma, so maybe I'm back to my original premise that the movement doesn't belong in this case. What do you experts out there think? Anyone have any info on a jeweler named Tisdall?