After a brief review of discrete Fourier transformation (DFT) — and fast Fourier transformation (FFT) — properties, two representatives of partial (narrowband) spectrum computation methods, the zoom FFT and a specific type of zoom transform, are introduced. With respect to the FFT, only the zoom transform sufficiently fits demands concerning memory space and computional speed. Moreover, it offers improved accuracy and applicability relative to the existing type of zoom transform. The described transform method, a link between an FFT and a single DFT sum, is compared with the use of separate DFT sums.