However, it's not the body that has to be parallel to the record surface (although, in a perfect world that would work). It's the stylus being 90 degrees to the groove that is important. Much harder to see, and even that is not entirely correct. What azimuth is really supposed to do is to minimize crosstalk between channels (or maximize channel separation). You really need to measure the output of each channel with a constant sine wave from a test record, one channel at a time.
But, for someone who can't or doesn't want to do that, then eyeballing a square cartridge body is probably the best method available.
