Full range of functions Exceptional sensitivity and accuracy for voltage, current, charge, and V/I resistance and resistivity (surface and volume) measurements. With the Models 6517-RH and 6517-TP, relative humidity and external temperature can be measured. Voltage source The internal 1000V V-Source can be configured with the ammeter to make V/I resistance/resistivity measurements, and to force voltage, measure current. Scanning The Model 6517A has an option slot that will accommodate an optional scanner card (Models 6521 and 6522). The instrument can also be configured to operate with an external switching system (i.e., Model 7001 or 7002) to scan external channels.