Cartridge Alignment Tool/Cartridge Protractor
An alignment protractor is used to find the correct distance from stylus tip to tonearm pivot.
When aligning a cartridge for tangency using the alignment protractor,
it is essential to remember that you are attempting to align the
cantilever (and, hence, the stylus), not the cartridge body. There is no
guarantee that the cantilever is perfectly aligned within the cartridge
body, so simply aligning the cartridge body will not necessarily
produce the desired result.
Furthermore, many cartridge bodies have non-parallel sides, making
tangential alignment of the cartridge body with the lines of tangency on
the gauge virtually impossible.
An alignment protractor is a plastic template onto which are printed the
null point(s) and lines of tangency against which the cartridge should
be aligned. The template is placed over the turntable's spindle (made
possible via a spindle-sized hole drilled in the template) and placed
against the platter.
Cartridge must be adjusted until the cantilever is parallel to the set
of parallel lines. And this should be achieved for both the indicated
points. When the cartridge's longitudinal axis is parallel with the
horizontal lines, tracking error will be at a minimum.