Fast Fourier transform
Such methods, however, are slow and clumsy to apply given the need for careful electrode positioning over a muscle of interest and the potential for misalignment of electrodes and inaccuracy. Accordingly, an initial hand-held system was constructed using multiple components with an electrode head that could be placed directly on the patient. The device featured an array of electrode plates, which could be selectively activated to perform impedance measurements in arbitrary orientations. The oscilloscopes were programmed to produce a compound sinusoid signal, which could be used to measure the impedance at multiple frequencies simultaneously via a Fast Fourier transform.