TT speed

Use an arc protractor.

Align stylus tip to arc for full sweep. Make parallel to only 1 grid, inside or outside, your choice. DONE. No guessing. No trial and error, no back and forth. The 2-point protractor is archaic and very inaccurate. 
 

I have 123 cartridges, so doing alignments is common. Takes about 5 minutes. I use Lofgren B DIN mostly. Sometimes Stevenson DIN. The Arc protractor is deadly accurate and quick. I use it for conical, elliptical, HE, LC, MR tips. I get no IGD. Haven’t heard that in years. 
 

For printing your free arc protractor, you need your pivot to spindle distance; it’s a spec for your turntable or you can measure it. Choose your alignment (Lofgren A/Baerwald, Stevenson, Lofgren B) EIC/DIN/RIAA null points, and print. Easy peasy!

You are connecting two parameters that are not related. The stylus tip does not need to know where it is on the surface of the LP in order to reproduce the frequency accurately. It’s essentially a point in space.

For any pivoted tonearm, the stylus will describe an arc starting at the outermost grooves and swerving inward to the right of the spindle as it heads toward the lead-out grooves.  When you use a typical 2-point protractor, like the Feickert, you can see this effect, because the protractor is helping you to locate the stylus and cantilever at each of the two null points defined by any of the 3 standard alignment algorithms.  By definition, the stylus tip and cantilever should be parallel to the groove or perpendicular to the center of the spindle, at a null point.  You have to rotate the protractor to set each of the two null points because the tonearm pivot defines one and only one arc upon which the null points have to be set.  Please try to visualize that if my words are insufficient.  Alignment can affect distortion characteristics, but it does NOT affect fundamental frequency.  Because no matter where you are on the arc, the cartridge is reproducing what is encoded in the grooves at that point.  When a test LP with a 1000Hz tone is created, it is done with a lathe that ideally automatically compensates for the changes in groove length (a spiral with an ever diminishing radius, heading toward the lead-out grooves).  Your rotating the protractor is just to locate each of the two null points, has nothing at all to do with speed accuracy.  So long as the platter maintains constant speed, 1000Hz is 1000Hz everywhere on the LP surface.

I think that what he is saying is that the stylus tracks an arc across the record, which means it is at some point slowly moving forward (retarding, in terms of time), then at the top of the arc, it starts to retreat (speeding up).  Both the slowing of time and the speeding up covers the entire side of the record and covers such a small number of degrees of arc (hence small fraction of one cycle of the record) that it has nothing to do with what can be perceived in terms of pitch change or timing.

Larry, You wrote, ...."at some point slowly moving forward (retarding, in terms of time), then at the top of the arc, it starts to retreat (speeding up)"  I think you would agree that although the velocity of the stylus tip does decrease as it moves from the outer grooves toward the inner grooves, just because path length is getting progressively shorter per revolution of the platter, this has zero effect on pitch, assuming a perfectly created test LP and a turntable with perfectly constant speed.

lewn,

Yes, of course this has nothing to do with pitch.