Most alternating currents and voltages are expressed in effective values, which are also referred to as RMS(Root-Mean-Square)values. The effective value is the square root of the average of the square of alternating current or voltage values.

Many clamp meters with rectifier type circuits have scales that are calibrated in RMS values for AC measurements. But, they actually measure the average value of input voltage or current, assuming the voltage or current to be a sine wave.

The conversion factor for a sine wave, which is obtained by dividing the effective value by the average value, is 1.1. These instruments are in error if the input voltage or current has some other shape than a sine wave.

CF : Crest Factor = Peak value/RMS value

DC = 1

Sine wave = 1.414