The precision DC Voltage Standard Source is a highly versatile reference source, designed to meet the needs of computer systems, production line testing, automated calibration, and standards laboratories. The instruments have a specified accuracy, and are traceable through a bank of saturated standard cells to the U. S. National Institute of Standards and Technology. Depending on the model of the instrument, resolutions of 0.1 ppm are attainable. The instruments are highly accurate references which can be used for calibration of digital voltmeters, analog meters, semiconductor analyzing systems, analog references for computers, analog-to-digital converters, telemetry and data acquisition systems, and where ever a stable source is required. There are no adjustments made during normal operation. The trims are made during calibration and are described under the calibration procedure. The circuitry is completely solid state made of discrete, hybrid and/or integrated circuits packaged on etched glass circuit boards. These are proven circuits, using derated components to insure long life and maximum reliability. The instrument is overload and short-circuit proof, and is fully operational in adverse environmental conditions. The Standard Source will drive a short circuit indefinitely without damage to the instrument, and will recover to rated specifications in less than 2 minutes. When used with a voltmeter, the source becomes a potentiometer for measuring DC voltages.