TT speed

Perform the demonstration in the last paragraph of my previous post.  Keep the platter stationary and move the stylus from the outer groove to the inner groove area and measure the distance from the stylus to the tape when located at the inner groove.  This is the linear distance the stylus will advance over the span of 15 minutes. At 60mm radius inner groove diameter, the circumference is 14.84".  Divide the distance from the tape by 14.84 for the portion of the total circumference and multiply by 360 to give you degrees.

The fact the stylus is CW of the tape proves the length of the groove used for playback increases as the stylus travels towards the dead wax area.  It's fairly easy to crunch the numbers and determine how much it advances on each rev. and therefore the change in pitch that will occur.

@phoenixengr 

Thank you.

Needless to say that a linear tracking arm is the exception here.

Thanks for the clearer explanation @phoenixengr
It is indeed a SFA* amount of shift.

* SFA is a UK/Au expanding to “Sweet F__ All”, which generally means is to the point of not mattering.

@holmz Yeah, that was weirdly interesting...

I have to credit Dover with causing me to re-think my prior position.  He simply mentioned that the cutting lathe is linear and the tonearm is pivoted (assuming a pivoted tonearm).  Rather than quantify the error, my simplistic approach is to start with the premise that the accuracy of the pitch (1000Hz) on this perfect LP being played on a perfectly speed stable TT depends upon the stylus remaining at a fixed point on the radius of the LP.  That, of course, doesn't happen with a pivoted tonearm; it touches the radius only at each of the two null points, assuming proper alignment.  When the stylus tip is off the radius, that represents relative movement of the stylus tip with respect to the recorded signal, which movement must change the pitch. Good thinking, Holmz.  Interesting discussion, too.