A stable voltage reference is connected to a two channel digital to analog converter connected to a range setting amplifier which provides the calibrator output. A microprocessor zeroes the calibrator by shorting the inputs of a zero amplifier to provide a reference zero towards which the calibrator is adjusted. It establishes the relative weighing of the two channels by adjusting one channel one increment up from zero and measuring the number of increments required by the other channel to return to zero. The microprocessor determines the gain change in the converter by establishing a bridge with known components and relating changes in the bridge voltage to the shift in gain.
