The Short-Time Fourier Transform Spectrum option in the Spectral menu or the Spectral toolbar furnishes Fourier spectral information for non-stationary data. Much as in the Fourier Spectra of Segmented Data option, the STFT is based upon a series of segmented and overlapped FFTs that occur across the data stream. In the STFT, the individual FFTs from these multiple segments are rendered as either a 3D surface plot (or a 2D contour plot). Both give a good indication of the time-frequency properties of the data series. The STFT can thus be used to assess whether or not a signal is stationary.
