Abstract: A power factor metering device. The power factor metering device includes a novel electronic circuit for deriving the power factor from a detected voltage and current. The device includes a current clamp that may be clamped onto any conductor of a three-phase or single-phase circuit. Voltage clips are used to detect the circuit's voltage. The current clamp induces a voltage that lags the detected current by 90 electrical degrees. An amplifier stage is coupled to the induced voltage through a low input variable resistance so that the input voltage to the amplifier stage may be adjusted to correct for errors induced in the phase relationship between the detected voltage and current. The output from the amplifier stage is input into a zero crossing detector stage that changes its output state each time the output of the amplifier stage passes through zero.