Cartridge protractor- the best?

Can someone please explain how any of these alignment protractors being discussed that use line of sight from spindle to pivot can be as accurate as a protractor that uses an arm and pin/nail (Dr. Feikert or Clearaudio) that locks the protractor to the arm's pivot point ? Seems to me using line of sight, it would be easy to be off by a few millimeter's either way, resulting in an inaccurate cart alignment.

Rockitman, The arc protractor is a replica of the arc the
stylus is supposed to trace (aka 'eff. lenght') along the
record. On the Mint tractor you have also the 2 nul points.
The spindle - pivot distance determine where one need to
drill the hole for a given tonearm. Ie the arc protractor
'assume' that the spindle-pivot distance is already correct. All 'ordinary' protractors are made with this assumption.

Regards,

In other words, as long as the protractor is on the spidle, no matter where the platter moves, the null point alignment lines will be correct ? This now makes sense to me...duh

actually on further thought, this doesn't make sense to me...The line of sight line on the protractor used to align the protractor to the pivot point seems prone to error. What am I missing ? TIA

Hi Rockitman, I am sorry if created the impression to know
anything about Feikert. This is not the case. I wanted to
explain the difference between spindle-pivot distance and
the arc protractor. From your reaction I may assume that
you 'got the picture'. However a mirrored protractor is not as easy to use as you assume. Our eyes are alas not 'omnipotent'. And those short cantilevers and styli which seem to hide from us are a p.in the a. So some magnifying instruments are needed. But you should try the
Mint protractor. I am in this hobby for 40 years and have
never seen something better. I have two of them for both of my tonearms (Triplanar VII and the Reed 2A).
Regards,