Three days of solid running and the fake belt delivers arguably audible wow & flutter.

I don't think the claim the belt is indistinguishable from the real thing in the eBay listing is valid.

It is obviously different. It looks far more glossy.

Can I tell you why it doesn't perform as well?

No. But it doesn't.

It is generally about 0.1% worse. That is over the line of acceptability IMHO.

Best solution is my probably 10 year old original belt running on the top of the spindle of the two Gyrodec 33 rpm options.

And here is where I found something very repeatable. Of the two 33rpm grooves on the motor spindle, the top one is more accurate.

This shows just how ridiculously sensitive such things are to precision machining.

Think about it. A tiny diameter spindle attachment is driving a relatively huge platter. Any manufacturing error on that spindle is observable by simply running an Android app on a OnePlus 13.

That said, that is state of the art mobile phone tech.

I am quite surprised how sensitive the phone and app are at doing the requested task.

Over loads of tests the trust in it inceases in a way I didn't expect.