This plastic protractor is a reliable way to ensure proper alignment of your standard half-inch mount cartridge of any brand. The goal is to avoid tracking error that especially occurs as your needle plays songs towards the inner part of the record. It is called inner groove distortion or IGD. This alignment is not to important on an entry level conical stylus but becomes progressively more important on higher end cuts of diamond tips as they approach the label or inner part of the record. Finer cuts become more pinched in the groove as the geometry of the tonearm creates an arc as it rotates towards the center of the record. This slightly rotates the facets cut on the diamond inside the groove which in turn can exhibit IGD; especially on difficult tracks.
TO USE: Loosen your cartridge mounting screws just enough to have to use firm pressure to slide the cartridge about in the screw slots of your headshell. Align the cartridge in the slots so the stylus tip lands at both the A and B "null" points on the tool as well as appearing aligned on the grids. See tool for drawings and grids. Retighten screws then double check.
WARNING: Don't rotate this tool around the platter carelessly while in use else you may catch the stylus tip and rip it out of the cantilever.