Abstract: The crest value and RMS value of a signal are measured. The ratio of the two values, the crest factor, is calculated to provide a measure of the signal wave shape. The frequency range and accuracy of a commercially available RMS converter is improved by providing an improved rectifier ahead of the converter's internal rectifier. This improved rectifier is also used to form the absolute value of the input signal. A peak detector then provides the crest value (absolute peak value). The crest value and RMS value are multiplexed to a computer having an A/D converter. The RMS value, crest value and crest factor can be calculated and displayed and/or stored by the computer.