Turntable Speed

@edcyn:

If the speed is way off, you should maybe buy another turntable with speed adjustment possibility. 

@ibjunkman:

I have never tried it on 78. Your iPhone would probably stay unharmed and on the platter if you laid it close to the center of the platter.

I really don´t understand your objection- would you rather not know if your turntable speed is way off?
The RPM app is just a simple and reliable way of knowing if your turntable operates at the right speed.
What could possibly be wrong with that? IMO it´s a basic parameter when playing vinyl.

If the speed is off then the pitch will be wrong. Especially noticeable on piano. Generally there are speed adjustments on motors, usually screws on the plinth under the platter. Sometimes you will see colored paint on the screws to mark their settings. They adjust the tilt of the motor and how the belt rides on the pulley which can adjust the speed. This along with a new oem belt and proper lubrication will usually correct speed problems. 

Those iPhone apps for platter speed are notoriously inaccurate at the level audiophiles want them to be accurate. What you get is the false satisfaction that you’ve seen a digital readout on the screen. I would recommend the KAB strobe system instead. Uses a large diameter strobe disc and a battery powered strobe light for constant frequency. But you don’t get a digital readout. Strobes built into turntables and any plug-in strobe light are subject to variations in AC line frequency.

@lewm, I have "RPM" on my phone and it seems pretty accurate. The Cosmos I have coming (hopefully soon) has a digital rev counter which I will compare to the phone. I made a hockey puck sized one inch thick platform with a center hole. It is placed over the spindle creating a dead center platform for the phone. It is made out of alder and is sized to match the weight of a 180 gm record. The phone is centered over the spindle. The phone also gives you wow and flutter. When it starts increasing it is time for a new belt.