Overhang

The first and most commonly known parameter involved in aligning your cartridge is known as setting the overhang. The technical term means the distance past the spindle that the stylus tip will reside with the arm rotated so that it's exactly over the spindle. Don't try this, though, as most arms aren't designed to rotate that far. There are a number of tools, mostly called cartridge alignment protractors, that aid in this.

Pivoted arms, due to their design, can only perfectly aligned at two points on the record. These are generally called null points. Linear tracking arms when properly adjusted, have an overhang of zero and will be properly aligned across the entire record's surface. Which two points you choose as null point will affect some of the distortions inherent in pivoted arms. The actual choice of the exact points requires that you estimate the distance from the spindle that your average record end. Fortunately, you don't really have to decide, as all of the cartridge alignment protractors are designed with pre-chosen null points. Among the 6 different tools I've used for this purpose, there hasn't been what I'd consider a significant audible when using any one than another. It seems far more critical that you align as precisely as possible using whichever tool you choose.