We present a digital sampling algorithm that uses two high resolution integratingvoltmeters that are synchronized by a phase-lock loop clock to accurately measure theactive and apparent power parameters for sinusoidal power measurements. The developedsystem provides high precision measurements of the root mean square, phase and the complexvoltage ratio of the ac signal with sophisticated algorithm which process the data infrequency domain. The system was designed to be used at the Korea Research Institute ofStandards and Science as reference power standard for electrical power calibrations. Thedetail uncertainty calculations have shown that the accuracy of the measurements werebetter than 4 μW/VA (for k = 1) and the level ofuncertainty was valid for the power factor range 0 ~ 1 for both lead and lag conditions.The system is fully automated and allows power measurements and calibration of highprecision wattmeters and power calibrators at the main power frequencies of 50 and 60Hz.