An excellent watchmaker should be able to open and close a watch back without leaving any marks. Very faint scratches may be acceptable in the bottom of a case notch if it has a sandblasted or satin finish, but steps should be taken to prevent those marks. There cannot be any visible marks or scratches on the top surface of the case back. Every necessary precaution should be taken to prevent damage, including using proper tools and using protective film between the tool and the watch. Case knives should be sharp and smooth. Wrenches should fit snugly in the notches and match the profile of the notch.