Turntable speed accuracy

Accuracy or sensitivity of speed monitor device should be proportional to (1) distance of sensor from center of rotate (longer radius is better) and (2) stability of the strobe at 60 hz per second. Ergo in theory the kab strobe (battery powered and not subject to AC line frequency variations) should be superior to timeline (batt power but v short radius) and to allnic (worst, with AC line power AND short radius). Admittedly, the kab is least convenient.

Tonywinsc, you have used the term "runout" several times. I believe this is intended to relate to the accurate centering of the record. But in all my years in this hobby I've only heard the term runout applied to the area at the end of the recorded material where the stylus rides a continuous circle. Am I the only one not understanding this term?

Now back to the basic subject of this post. It seems to me the motor/bearing/platter have four tasks:
- providing a stable platform for the record,
- not introducing any noise which may be picked up by the stylus,
- rotating the record accurately at the desired speed (this might be considered the overall average speed), and
- maintaining that speed through the mili-seconds when interference might occur from imperfect motor rotation, power line fluctuation, stylus drag, etc.

If I am correct, it is the last of these tasks which may be the most difficult to achieve. I've never seen a Timeline, only a demo video. But I have two comments. First I agree with Lew that the distance to the sensor mark would be important. But secondly if the mili-second interference does not occur at the point when the sensor mark is reached the error may not be noticed. In other words the speed might have recovered by the time the sensor hits the mark. Does this make sense or am I misunderstanding something basic here?

Dear Lewm,
the Allnic SpeedNic is battery powered and not so bad as you think...
also it allows adjusting during play.
I am not selling this product :-)

Rugyboogie,
you are in very comfortable situation with one running turntable ;-)

best @ fun only

Rugyboogie, I meant with one belt drive TT, sorry!

best @ fun only

Runout is the measurement of the eccentric motion in a rotating body. What I have been talking about in terms of a record is that the center axis of the record grooves are not matched precisely to the center axis of the platter. (Shaft runout would normally be measured in V-blocks in a lab and would consist of a combination of roundness as well as straightness of the shaft.) Additionally, the platter can have some runout- hopefully that is nearly unmeasurable considering the cost of some of these platters. The best way to measure the runout of a record would be to measure the swinging motion of the tonearm when it is playing a round groove at the inner diameter of the record. It would be difficult to measure while playing in the music groove since the tone arm is continuously moving inward towards the center of the record. The OD of the record is likely not that round and not necessarily tied dimensionally back to the music groove. I would say that if you can discern a swaying motion in the tonearm with your eyes as it is running in the music groove, then the runout is probably high. This was the case with my test record. But even then, I could hear the Wow only when playing pure test tones.