A waveform describes the variation of a quantity with respect to time. The necessary measurements to determine a waveform are normally carried out and presented in one of two ways: the amplitude may be presented as a function of time (time domain), or an analysis may be given of the relative amplitudes and phases of the frequency components (frequency domain). Although the simplest instruments measure and display the information in the same domain, it is possible to convert the results from the time domain to the frequency domain and vice verse by mathematical processing.