Tired of pulling out a strobe disc every time you want to check / tweak the speed of your table? Now there’s an app for that. RPM (iPhone / iOS 8.1+)uses your phone’s built-in gyroscope to quickly and accurately measure the rotational speed of your platter.
In tests verses platter markings or dedicated strobe packages I’ve found the app to be spot on, to the point where it has become my go-to measuring solution (note — this has been on the iPhone 6/7, your mileage may vary).
There are multiple handy features including the ability to set sample rate, a graph of speed variance within the each rotation (wow and flutter) and a display lock which keeps the readout facing you at all times regardless of the position of the device.
While the app is free, I recommend opting for the upgrade (US $2.99) which allows for continuous operation so you can monitor how speed changes from startup to steady state operation.
You can check out RPM on the Apple App Store.