The Keithley 642 Electrometer is a direct-reading MOSFET-based electrometer for sensitive measurement of current, voltage, or charge. Its current measurement range is 10aA to 200nA with typically less than 1mV voltage burden. Voltage reading capabilities are 10V to 10V with 10,000 Tohm input resistance. Charge can be measured from 800aC to 100pC. Maximum sensitivity is obtained when using the CHARGE mode to integrate current applied to the input.