I have just encountered a quite unusual (to me) Rolex Oyster Perpetual calibre 1520 movement, (automatic, of course), with only 17-jewels. I have only ever seen the 25-jewel version, and that is what is shown in the catalogs and parts books that I have. I have never heard of such a movement, and of course have never seen such a thing, until now. The movement is in a Submariner model 5513 from the mid 1980s. I'm sure it has been on the owner's wrist every day for the last 20 years, so you can imagine the condition! And the automatic winding is (naturally) totally worn out! Has anyone else seen such a watch, and do they have an explanation for its existence?