The paper gives an account on a new power measuring system, based on digital sampling, which was developed by the National Institute of Metrology (INMETRO) of Brazil. The goal of the project was to achieve the highest possible accuracy at the presence of considerable harmonic distortions, to guarantee full traceability to national standards and to minimize the costs of obtaining a high quality reference system. The system facilitates the calibration of commercialized electronic wattmeters, watt-hour meters, as well as the analysis of non-linear loads, resulting harmonic distortions in power systems