TT speed

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. 

I suppose that since the speed variation from the stylus movement angle is lower than most W&F specs it is not really a concern.

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.

^Well put^ sir, that is exactly what I was trying to say.

  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.

The fact that the cartridge moves some number of degrees of platter rotation, effectively would be the same as running the platter bit faster or slower… assume that the patter was, say, perfect in its speed,

The fact that the platter speed variation is greater than this Mathematical tracing delta makes it somewhat a moot point.

OP, Though I couldn't get what you were describing, it finally came clear when larryi posted. Whether it matters or not, it still is something that I had never considered before. A new thought for me. I very much appreciate discussing or learning about these sorts of topics. 

Thanks @4krowme it was great that Larry could describe it better.

I felt like a scratch DJ moving the platter back-n-forth over the protractor when it occurred to me.

So it is more of interesting… but not entirely relevant.

If we had a short recording where the tracks were widely spaced, then the error gets bigger than say a super long “LP” record with more tracks being closely spaced.