Feickert Protractor - anyone use one?

Good point Lew.

Actually I've utilized my Dennesen to precisely locate the spot to drill to mount an arm.  With the P2S dimension given by the arm manufacturer and a steel metric ruler I set that distance on the Dennesen.  Then placing the alignment plate on the spindle I can swing the device to identify the arc on which the arm should be located.  From that I chose a position on that arc which best accommodates the arm and mark that point to drill.

All this seems obvious if anyone owns a Dennesen or similar alignment tool, but those considering buying one may not realize this extra benefit of this type of alignment device.  

I guess I did not make my point very well, but for me the beauty of the Feickert is the cross arm that is graduated in mm, with a vertical spike at the far end that can be set down on the pivot point exactly.  If you measure P2S with a conventional ruler of any kind, there is that awkward requirement to estimate that you are "over" the desired location of the pivot; if the ruler does not lie in a horizontal plane parallel to the pivot point on the tonearm or the blank tonearm mount, there will of course be an inaccuracy due to parallax.  The Dennesen and even the original version of the UNItractor, incorporate cross arms that are not marked in units of distance.  (I am guessing that this fault has been remedied in newer versions of the UNItractor, because I think I see in photos that the SMARTractor includes a crossarm marked for distance in mm; the SMARTractor is less expensive than the UNI.)

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.