I have a similar RPM app for my Samsung phone, and I find it to be fairly accurate. A lot of people just lay their phone on the platter and use the app that way. Doing so that way seems to show a variation of about 0.2 rpm, dipping down to 33.1 or even 33.0 rpm for a split second. However, if you have a record weight/clamp and are able to center the phone on top of the clamp, you get a steadier reading. On all three of my turntables, it's generally spot on at 33.3 rpm. It may vary a smidge between 33.3 and 33.2, but leans more towards 33.3.
