tonearm mounting and alignment

I should have titled this "cartridge mounting and alignment." My mistake.

You shouldn't be aligning the body of your cartridge, whether it's square or otherwise. The body of the cartridge doesn't trace the record grooves, so why align it?

You should be aligning the cantilever (ideally, the stylus, but that's too small to see). You need to align the piece that's actually tracing the grooves.

Yes, a better protractor would help you do this better. Search the forum archives. We've discussed the pros and cons of different protractors several times.

Doug, I appreciate the clarification. After searching through the forums, I realize I've been mounting cartridges poorly for years. I feel pretty stupid about that. I need a protractor. Do you have any recommendations?

I'm using DB Protract.
Its pretty clear and fairly easy to use. What you want is something that visually easy to align.

Another alternative is to get the Freckhart(spelling) alinement jig which is even more comprehensive.