Dumb VTA Question

Sorry ... I have a dumb question about setting VTA. I own a VPI Classic TT which has "VTA on-the-fly" capability. My cartridge is the Lyra Kleos. When I mount the Kleos, the last adjustment is VTA. I start by setting VTA so that the tonearm appears horizontal. Then while I'm playing a record, I raise the tonearm and then lower it until I like what I hear.

Ok ... that's what I do. But here's the dumb question. Some vinyl buffs talk about setting VTA at 91.5 degrees, or 92.5 degrees, and the like. How the heck can someone know the degree of VTA adjustment with such precision?? Is there a tool or special protractor that permits such close adjustments?

Thanks for the education.

BIF