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A direct-current, degenerative, slide-back, vacuumtube voltmeter employing standard potentiometer design principles is described. The voltmeter is completely self-calibrated upon construction. By adjusting the voltmeter to the same reference balance condition for all voltage measurements, the grid current is readily reduced to less than 10-9ampere. Voltages in the range from 1 to 100 volts are read to four significant figures in the experimental model of the voltmeter.