This app is great! The FFT option for the magnetometer is marvelous use of the existing smart phone sensor to create a rudimentary mobile EMF scanner. Try using it near a 3ph electric motor, and you'll see the produced disturbance in the magnetic field! Id like to see an option for the FFT to be able to set your own frequency range for the experiment, allowing you to eliminate frequency/frequencies you don't want to saturate the graph.