As I am still debating if I want to get the ERT-300, I run into this "freqmess", a XP application that picks up the tune from a microphone. The user has to hit or tap the racquet center then let the microphone pick up the tune. When it works, the results are reasonably distributed in the expected range. When it doesn't, most likely it was that tap didn't go well. lol!
It seems it is like eagnas t-001, or racquet tune for ipad / iphone.