The Chopped Voltage Reference provides two precise voltages for differential amplitude measurements. This calibration fixture is specifically designed for use with the Tektronix Type 1A5 Differential Amplifier in measuring television waveform amplitudes. The output waveform is derived by mechanically switching between the two precision voltage sources. Using chopped voltages instead of a fixed DC level eliminates long-term level shifts in differential amplifiers usually caused by junction temperature changes. Because of loading effects of external circuits connected to the Chopped Voltage Reference Output, corrections will have to be used to determine the actual settings of VOLTS or V2 VOLTS dials for the desired output voltages. The table, Section 10, corrects for 1 megohm loading.