Valhalla Scientific's Model 2701B Programmable Precision DC Calibrator is a highly stable precision DC voltage source. Front panel switches permit selection of output voltages from 1 microvolt through 1,222.221 volts in four ranges, with a resolution of one part in one million. The instrument uses a precision reference for output control. The voltage level of this reference is dependent on the duty cycle of a digital pulse generator which, in turn, is controlled by the front panel voltage selection switches. Since this technique eliminates the shortcomings of-conventional resistive voltage dividers, the accuracy and stability of the instrument are independent of switch control resistance. Digital control of the pulse generator greatly simplifies remote voltage selection through an optional IEEE-488 interface.