Most accurate IOS app for turntable speed check

Again, I thought the subject is how to measure speed, not how to maintain correct speed.  I agree with Elliot; it is not so important to maintain bang on 33.333 rpm as it is to maintain constant speed. I think we/I am more sensitive to speed varying during play than I am to slight errors in constant speed.  But the OP wants to measure speed per se.

Very easy to do with any laser tachometer you 

can buy online. You need some reflexive tape. Should be more accurate than an iOS app.

OP was asking about recommendations for "Most accurate IOS app for turntable speed check". Well, as @dover correctly pointed out, these apps are not accurate:

RPM and other apps I have tried are not accurate. Results are inconsistent. They are only good for entertainment - not calibration.

Just for giggles, I once installed RPM on two phones, then placed both phones on a spinning turntable with the apps running. The speed readings were different. What’s worse, the delta between the two readings was not constant.

My uneducated guess is that the inaccurate readings are a function of the phone hardware rather than the app itself; but in any event, these apps are not fit for calibration.

@lewm 

I agree, constant speed is important, wavering even very slightly is bothersome.

when I hear streaming at friends houses, and female voices are just wrong, and we play their LPs they agree, I never thought about it, but could speed be an issue in streaming?

The streaming that sounded wrong, Eva, Ella, Nancy Wilson, I assumed it was just poor quality content.

I played a friend’s cartridge here, he didn’t know the proper settings, we had it wrong, same thing, female voices, i.e. Annie Lennox, ... just didn’t sound right. We both agreed my cartridge got the voices right.

I looked it up, found the correct settings for my SUT, he brought it again, all was right.

That had nothing to do with speed.

I can’t say it’s super accurate but the Grooved app definitely close and it is VERY easy and free. When I have a chance I will measure it against my KAB strobe and report back.  It’s nice because it listens to a record as it is playing and checks it’s pitch and tempo against standards (if I remember correctly). I’ll revert later this week with my accuracy check.