I have two of these, differing slightly only in the case. This one has a hinged back, the other a snap-on. The one shown I just completed a service on and bleached out the numerous hairline cracks in the dial. At present (6 hours on) it seems to be running well with plenty of balance amplitude. I haven't got round to looking up the serial number or even the cal. so I'd appreciate anyone who recognises it informing me. What's puzzling me is that it looks as though it must be a PW conversion however there are no witness marks on the case as far as I can tell. I've been working on a few early Walthams recently and setting aside the infuriating keyless work, they seem really robust for the period. Roy EDIT: S/no 17967327 appears to indicate 1910, which is about what I suspected.