The 2509 Digital Wattmeter uses a unique YEW-developed feedback time division multiplier, and the unit has a frequency range of 40 to 400 Hz and is accurate to 0.5%. The voltage range of 250V and the current range of 1 to 10A make this instrument suitable for power measurements over a wide range of general-purpose electrical equipment. In addition to wattage measurement, an outstanding feature of the 2509 is its ability to make highly accurate measurements of true voltage, current, or wattage of distorted (non-harmonic) waveforms by means of an algebraic effective value-to-DC converter circuit.