The Keithley Model 181 is a highly sensitive nanovoltmeter with a large, easy to read 5½ or 6½ digit display. The Model 181 is unique in that it combines microprocessor technology with a new concept in low-noise, high-gain front ends, resulting in a programmable instrument with sensitivity down to 10nV. The Model 181 provides highly accurate, stable, low-noise readings on seven ranges for DC voltage measurements between 1OnV and 1OOOV. The mV ranges use a special low-thermal input connector, while connections for the higher voltage ranges are made through two S-way binding posts. Additional versatility is afforded by the inclusion of an IEEE-488 interface which allows the unit to communicate with other instrumentation.