@rauliruegas is absolutely correct. Most tonearms are not at their specified spindle to pivot distance. They are off by several mm which throws the Mint out the window. There are way too many ways to create error when drilling for the tonearm. SME took this into account when they created their famous tonearm base.
In order for a protractor to be as accurate as possible the lines have to be vanishingly thin and there has to be a little divot to place the stylus in. The SmarTractor is a great example. It also gives you a choice of alignments, Lofgren B being the best for modern records. The SmarTractor also allows you to accurately measure the spindle to pivot distance. So, if there is room for adjustment you can get it right on target.