..The "0" shows the number one piston at TDC..(top dead center)..The marks show the degrees of the number one piston at BTDC..(before top dead center).. or on some emission engines ATDC.(after top dead center)...It all relates to the camshaft and distributer timing...........There have been so many balancers (dampners)..made for each application it can be a nightmare.........A vacuum gauge works good to aid in setting the running timing...Always use manifold vacuum...In other words connect it below the throttle plates.....................................I know.....Lets ask Streets...He's got info up the ying ying...........Hey .!! Streets.....you reading this.???......What is the best way to get the correct dampner anyway.?????.....