He means adjusting the screws / levers that regulate how much or how little of the wound spring to let out at a time. Slight changes to that tolerance can "adju

He means adjusting the screws / levers that regulate how much or how little of the wound spring to let out at a time. Slight changes to that tolerance can "adjust" how fast or slow your watch keeps time. You can pop the back of a mechanical watch off and adjust these parts with a tweezer and put it back together, then see if the time is kept better. There's also machines that can detect the time keeping accuracy to help you adjust a watch's timekeeping this way