turn crank till the dampener slit is at 15 BTDC. install stop till it firmly contacts the piston. turn crank CCW till the piston contacts the stop. if the slit is at 15 ATDC then the slit is dead on. I would also measure how much slack the chain has & measureing that at the dist rotor will also include dist intergear/lower tang slop combined with the chain slop. Check by turning the dampener CCW carefully till the marks are at 15 BTDC (keep the chain taut in that direction) then turn the crank back CW till a helper hollers that the rotor JUST moves (use the dial indicator for that). that distance on the dampener in degrees is that total slop amt