The Keithley Model 148 Nanovoltmeter conveniently measures dc potentials from 10 nanovolts (10 x 10-g volts) to 100 millivolts full scale. It makes accurate and sensitive measurements without painstaking methods often previously required. Meter accuracy is 2% of full scale on all ranges. Noise is less than 1 nanovolt peak-to-peak on the lo-nanovolt range. Zero drift is less than 10 nanovolts per 24 hours after warm-up. On the three most sensitive ranges, line-frequency rejection is greater than 1OOO:1.