A calibrator for Watt and Watt/hour meters, Model MSB100 provides reliable, accurate traceability to N.I.S.T. and other national standards worldwide. For use as a primary Watt or Watt/hour reference meter, the instrument has four voltage input ranges from 120 to 640 vac and five current ranges from 50 mA to 5A with optional current ranges of 10A, 50A and 200A. Accuracy is 0.005% for power and 0.015% for energy maintained regardless of phase angle to greatly simplify power measurements at near zero power factor. The instrument's digital I/O connector allows direct connection to Watt/hour meters equipped with a pulse output. Meter outputs can be compared using the MSB100's built-in comparator. No additional test equipment, computers, or complicated test setups are required to calibrate the meters. IEEE-488 and RS-232 remote interfaces are included, and optional 10BaseT Ethernet interface is available.