Electrometers from Keithley Instruments can be compared to digital multimeters (DMM´s) but with extreme high input resistances for measuring high impedances. With Electrometers, voltage, current, resistance and charge can be measured without burdening the source. The typical input resistance of an Electrometer (eg model 6517B) is about 200TΩ (=2x10E14 Ohm).
The Nanovoltmeter from Keithley Instruments is ranging on the other end of the impedance scale. In a 10mV full scale range 1 nV (=1x10E-9 V) resolution is achieved. With Nanovoltmeters all kind of sensitive low voltage or super conductivity measurements can be done.
With all these sensitive instruments from Keithley, extreme low currents or low voltages can be measured for the demand in modern semiconductor industry, nanotechnology or material research.