Feickert Protractor - anyone use one?

Amen to that lewm !
There are a FEW TT's with something sticking up from the pivot you can sight on with a 50 buck Geo-Disc and get 'er done but not many .

Lew, another method which I've done over the years is to create a template out of sturdy stock such as a file folder.  I have basic drafting skills so can lay out a line with the exact center hole for the spindle, the P2S distance from that to arm pivot point, and then mark that with a vertical needle.  Rather than attempt to cut out a circle for the spindle I found a simple X cut with an X-acto allows the template to be fitted over the spindle.  Anyway, it worked for me.

My above post assumes the arm does not have a factory mounting template.  Buying used arms typically eliminates that convenience.

I use AccuTrak arc protractors for my arms.  I have a TT where I can adjust P2S distance easily.  I think this point was made earlier, with Arc protractors you don't need highly accurate P2S measurement, just need accurate enough to get within the overhang adjustment range of the headshell. When you are on the arc you have the overhang correct.
For most cartridges where the cantilever is visible, the AccuTrak allows for very precise adjustment of zenith. Especially with a magnifying glass.  For some cartridges, a mirror would be helpful.  All this being said, if money grew on trees, I would enjoy using the SMARTractor which seems to offer all these features.

I have been graciously schooled on another forum as to the importance of the spindle to pivot measurement.  An overhang arc depends on its centre Re: pivot point to be accurately place in the right location.