Direct drive vs belt vs rim vs idler arm

All measurement equipment has an accuracy and a repeatability factor. As engineers we have to measure our measurement equipment and it can get frustrating and confusing at times. Like the old saying: "A man with two watches is never sure what time it is." I still think the weak link is the test record. Eccentricity tolerances of the center hole is the first and foremost issue; but another problem is flatness. Any variation in the surface of the record is going to cause a speed change at the stylus- ie. the linear speed of the stylus in the groove. I see the same things. The longer I play the test tone the higher the values. The better that I center the record on the platter, the lower the values that I see. Overall, I have results that vary from 0.01% up to 0.04% with my turntable. I have my own 25 year old test record. Maybe the 7" disc is better with respect to flatness as compared to my test record. It would be nice to find a 180g test record.
As for the iPhone app, it occurred to me that I have a test CD with a 1kHz test tone. So I just did a test with the CD. The app reports a mean frequency of 1000.7Hz. The line is dead flat. The deviation is 0%. Short or long test had the same results; but here is an interesting observation. First, I held the iPhone in my hand and the result was 0%; but the raw result showed waviness in the line. Very small peaks and valleys. So I placed a small table in front of my speaker, placed the iPhone on that table and reran the test. This time the line was dead flat, but still had a small wiggle right at the beginning where I had to hit the start button on the screen. So as I suspected before and just saw, holding the iPhone in your hand while recording will cause additional variation. I suspected that before and always rested my iPhone on a table for the tt tests. This just proved my suspicions.

Also, it looks like to me that the app is reporting peak values, it is not averaging. I noticed that while looking at the handheld CD test results vs. resting the phone on a table. So like I was saying, one blip on the test record, like a high spot and the resulting values will increase.

As I do the tests with the 1350Hz Test Tone.....I can graphically see the frequency on the iPad App moving backwards and forwards equally about the 'mean' frequency.......so that the average mean frequency comes in very nicely on the Data......but the wow and flutter is high.
This is definitely caused by the off-centre hole on the 7"" test record.
I suspect Lespier does not use the Feikert 7" Test disc.....or if he does.......his is a 'good' one?
As you say Tony.......I think our turntables are testing the 'test' equipment?

Back to the Timeline for me :-)

I know what you are saying. Our simple measuring equipment has limitations. If you stare at this data too long and try to interpret something that is just not there, then you will start to see fairies dancing on the screen. I think the app is perfect for dialing in platter speed and it gives us some assurance that our turntables are holding speed an order of magnitude better than the capability of the records themselves. And because of that limitation built into the records, the app is limited on accuracy probably to the 0.03%-0.05% range. Keep in mind too, like I said before; the Timeline needs to run for several hours on your tt in order to get a reasonable data set for evaluation. One side of a record play, 600 rotations, is not enough data points. You need thousands of rotations to conclude anything in the 0.01% range or else you will be seeing those fairies dancing around.

Halcro
Do you have any theories other than eccentricity as to why the results with the Feickert are inconsistent?

Thanks