As long as one attains perfect tangency at the chosen two null points, the proper offset angle and pivot to stylus distance has been attained (i.e., proper alignment). The use of the Feickert spindle-to-pivot measuring arm is merely a convenience. Once you know the distance, you can select the proper arc where the same sort of tangency points are marked. The convenience comes from the ability to firm lock the platter/alignment tool in a single spot when making the tangency adjustment. Unlike simple two point protractors, you don't have to rock the platter back and forth when moving from one of the points to the other. Some people have a very hard time figuring out which way they have to move the cartridge to adjust the overhang when they are also moving the platter when making the adjustment so they can never achieve agreement at the two points. With the Feickert, one first puts the tool into perfect alignment (needle point over the pivot center) then one locks the tool in place by putting some kind of wedge under the platter so the platter doesn't move. The distance measure tells you which curved line you should use to make your measurements. The correct overhang (stylus to pivot distance) will be achieved when the stylus sits in the tiny dimple on the correct curve for either of the two measurement points. This distance should be the same for either measurement point if the correct curve has been chosen. Once correct overhang is achieved, it is easy to twist the cartridge to achieve tangency as well.
