You say, "AnalogMagik software does measure instantaneous speed. I think Fremer may use it, or possibly have some other software by which he determines the variability and stability of speed control of the turntables that he evaluates."
I was speaking of fundamental physical constraints, not marketing claims. Speed is defined as displacement / time. We’ve known since Planck that the world is quantized, not infinitely smooth. Hence instantaneous speed is a theoretical concept which cannot be physically realized.
It remains only to specify how close a given measurement is to the ideal. Visible light brings constraints in terms of wavelength. Markings to denote the boundaries of the average are required - how finely are they drawn? What is the sampling rate? Each of these introduces quantization AND each of these introduces its own source of error.
That’s all. My point is simply, "How coarse are those averages, and even if they were analyzed completely, what can those averages tell us?" I suspect that our ears/brains, the result of a billion years of evolution (with survival at stake), tell us more.

