The Working Standard WS 2x20 is a single-phase (WS 2120) and three-phase (WS 2320) precision reference meter for electrical power and energy measurement, dedicated to on-site meters testing. The device can be used also as hand-held unit for local data exchange with smart meters (programming and data readout of meters). The device is designed for operation in single, two and three-phase systems, where it evaluates and displays all individual quantities per phase and cumulative three- phase ones as well. Universal inputs can be equipped with any combination of interchangeable precision voltage sensors working up to 600 V and current sensors working up to 6000 A or more. Measurement is based on precision A/D conversion and DSP technology and enables accurate high-speed real time evaluation of all main and informative quantities. Beyond measurement of power, voltage, current and phase the device indicates voltage sequence, evaluates active, reactive and apparent energy and measures distortion and wave-form of measured signals. The device can generate any programmed energy proportional or constant frequency on the impulse output. This unique feature allows precision error evaluation with minimum integration period. The device is equipped with integrated error calculator and meter scanner capturing LED, DISK or Closed Contact output of tested meters and snap switch for simple manual testing. Multiple optical scanners can be arranged to wireless network for simultaneous testing of complex distribution networks with single Working Standard. Synchronous differential mode of energy consumption is also possible. The device can be supplied from internal rechargeable accumulators, from external power adapter, from car outlet or optionally also from measured voltage circuit. Software for MS Windows enables transfer and presentation of measured data in PC. Optional portable printer enables on-site printing of results or actual display content.