Best protractor for aligning to cantilever


I am trying to find a protractor that makes it easy to align the cantilever rather than the body to a grid. I have a cartridge where the cantilever is not perfectly parallel with the body. It's a Grado and the plastic on the front of the body is not seated correctly or something. The cantilever is parallel to the back, but the front being out of alignment makes it hard to align to the body. It is merely a cosmetic issue so I would like to keep the cartridge.
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I am rediscovering vinyl and wish to set up my (Micro Seiki) arms correctly, but am only familiar with the basics. I'm not even sure what a protractor is supposed to do, or what the subject means. I would appreciate suggestions on how to proceed. Cost is a consideration.
I just got word that a mint lp was shipped to me from Hong Kong yesterday. It's for a Linn Sondek 12 w/ a Basik tonearm. Since Linn tonearms are the same length, I can upgrade and still use the tractor.
Polk432 -- Yip at mintlp is quite helpful and has me researching the subject at informative sites before I use his services. I have one well-documented vintage arm and a rare, undocumented one, so this should get interesting. Thanks!