Assuming my test tape is stretched (I doubt it , as it would have to be even
stretch the whole length).
I normally test speed monaurally so the beats are unmistakable. That is 1KHz
test tape output and floating accurate 1KHz sine signal both fed into one
headphone cup. Easily gives 0.1 percent resolution (assuming test tape is
ok).

If I record accurate 1KHz tone onto a blank tape for exactly ( to human
reaction time accuracy) 100 seconds. Then replay for beats of 1Hz or so and
output lasts for 100 seconds +/- reaction time then is the speed correct? I
suspect that repeating this process with the speed regulator changed , say 5
percent, would also give "correct" speed, that time also


Does anyone know how much effect types and thickness (play duration C30 to
C90) have on replay speed perhaps in conjunction with too soft or too hard
pinch wheel rubber ?