Input the data points of any waveform (assumed repetitive) and it computes the Fourier transform. Or give it the transform (Fourier co-efficients) and it computes the wave. You can even do two independent waveforms, plotted X vs Y (such as Lissajous figures). Sample run contains such an X-Y plot in the shape of Mickey Mouse; by taking various numbers of harmonics into account, you can see Mickey transform from an egg into a mouse.