Turnable database with TimeLine

Don,

Then listen closely at these different speeds, on records that have light and heavy modulation, and try to hear changes in sonics.

I think you're talking here about speed 'consistency' rather than 'absolute' speed?
I have no doubts that you are correct in the fact that if a turntable is running CONSISTENTLY fast or slow....and can cope with 'stylus drag'....the resulting sound will be undistorted and one could not really tell the difference.
In fact...the TT-101 has the facility to adjust the speed either UP or DOWN in 4 Hz increments so that one can match the relative 'pitch' of the record with an instrument that one might wish to play along with.
The only problem here....is that we don't have a Timeline which can alter 'pitch'....so that consistent speed of a turntable under stylus drag can only be verified by the Timeline at exactly 33.33rpm.

Not to beat a dead horse, but if one were to measure precisely the left or right movement of the laser spot over time with no stylus drag and then do the same thing in the presence of stylus drag, one could in fact establish that the tt is capable of maintaining some constant speed in spite of stylus drag, even if that speed was greater or less than 33.33 rpm.

Lewm,
After reading this thread for weeks now, this is exactly my question, and what I have not seen addressed in any of the posts so far. If it has been addressed, my apologies.

If a turntable slows down for a very brief moment due to the stylus drag and the Timeline registers it by shifting the laser spot but then remains constant, how relevant is that drag save for the very brief moment of the stylus settling in the grooves and the turntable adjusting its speed?

I think the confusion lies in trying to use the Timeline, which shows average speed over any period of time, to evaluate momentary, micro-variations in speed due to stylus drag. The timeline can only infer that speed is varying once the stylus is in the groove if the laser mark drifts. The problem is you can't know if the drift is due to speed being something other than 33 1/3 exactly or if speed is actually changing during play. The only sure way to measure the effects of stylus drag on speed for a particular tt is with a very fine tachometer.
Think of driving your car. You time yourself from point A to B and knowing the distance determine your speed. That is average speed. If you want your speed to be exactly 30 mph then you must leave and arrive within a specific time interval. The thing is, you don't know what your speed variation is between points A and B. In order to know your speed variation you must watch your speedometer. The speedometer is giving you instantaneous speed. Showing your stopwatch to someone as proof that you drove exactly 30 mph between A and B doesn't prove that your speed was a constant 30 mph. Maybe you went up a hill and dropped to 25 and then down a hill and got up to 35 for a moment averaging out to 30.
The timeline is like a stopwatch giving you average speed.

Agree with Tonywinsc. I think the KAB measurement makes more sense for average speed and constancy of speed.