GENERAL. a. The Keithley Model 610C Electrometer is a versatile, completely solid-state instrument which measures a wide range of dc voltage, current, resistance and charge. The Electrometer's input resistance of greater than 10^ ohms is the result of extensive instrument development with high input impedance transistors. The Model 610C has all the capabilities of conventional VTVMs, but it can also make many more measurements without circuit loading. b. The Electrometer has eleven voltage ranges from 0.001 volt full scale to 100 volts, twenty-eight current ranges from 10 ampere full scale to 0.3 ampere, twenty-five linear resistance ranges from 100 ohms full scale to 10⁻¹⁴ ohms, and seventeen charge ranges from 10⁻¹³ coulomb full scale to 10⁻⁵ coulomb. c. The Model 610C employs matched insulated-gate field-effect transistors followed by a transistor differential amplifier and complimentary output stage. A large amount of negative feedback is used for stability and accuracy.