Thift buy (not particularly cheap - but a good buy I think). I would appreciate any information as to how old and what mechanism I should expect to find. I'm being cautious about opening. I assume if 20Atm should be harder than average to remove back and no easy notch seems apparent for opening. Don't want to scratch. Running quite accurately right now. Signed Champion band that I assume is original. Crown is not signed. Should I assume crown is not original? Thanks for any opinions and information.