The Fourier Spectra of Segmented Data option in the Spectral menu or the Spectral toolbar is the traditional periodogram with some additional Fourier spectral information. For non-stationary data, it is also the precursor of the Short Time Fourier Transform. This option computes an averaged frequency spectrum by taking the individual FFTs of multiple (and usually overlapping) segments of the data stream. The segmenting results in a smaller size data record, and consequently in a reduced spectral resolution, but the averaging reduces the variance that would arise in a single FFT.