Most accurate IOS app for turntable speed check

The responses jumped from best way to check speed to best way to maintain correct speed. Yes, the roadrunner is an appealing way to monitor speed because it gives the false comfort of a digital readout to 3 decimal places, but what is the evidence that the SOTA or Phoenix Engineering systems are superior to “most any” DD? I use both, by the way. Am happy with DD and PE on my Lenco.

Nothing hokey about the Roadrunner.   I used my existing arm and cartridge from my previous SOTA , it is a marked improvement .

Its solid speed is why it sounds so good, I am confident of that