We have developed the WT1600, a high-precision, wide-bandwidth power meter. The WT1600 can measure DC and AC signals from 0.5 Hz to 1 MHz with a basic power accuracy of 0.1%. With the maximum of six input elements installed, a single WT1600 can measure the efficiency of a three-phase inverter. In addition to the functions of conventional power meters, it has wider ranges and various functions including waveform display. This paper gives an outline of the WT1600.