Hi, For the Y-axis, it depends of the input data binaries. I mean, if these come from a voltage signal or a collection of data or a sound signal, etc. It's necessary to know the factor conversion the voltage values, for example... And for the X-axis, that represents the axis of frequencies, and its posible to reconstruct until the nyquist order of the harmonic frequency (FS/2). Also it's important, the lenght of the input data, it's a power of 2, since algorithm FFT gives a fast and optimal result. Then connect the output to a "Waveform Graph" Display, on the front panel. I hope this help. Bye..
