Abstract: Measurements of complex permittivity using transient techniques and Fourier transforms require computation which can be lengthy. In the invention, a synthesizer generates a succession of waveforms each containing a small number of harmonically related frequency components. These waveforms are applied to a capacitive potentiometer formed by a reference capacitor and a sample head. The voltages across the potentiometer and the sample head are passed by way of an analog-to-digital converter to a microprocessor which calculates Fourier transforms and indicates permittivity versus frequency. By limiting the frequency components, the computation time is reduced and a quick scan to find spectral regions of interest is possible. These regions can then be examined at higher resolution by changing a clock frequency which determines the generation of the frequency components.