Jandel Engineering Limited offers the RM3000+ for use in making four point probe measurements. The RM3000+ can supply constant currents between 10nA and 100mA, and measure voltages from 0.001mV to 1000mV.
For sheet resistance measurements the quoted range is 1 milliohm/square to 1 x 108 ohms/square. Measurements outside this range are possible but with possible reduced accuracy.
For volume (bulk) resistivity measurements the quoted range is 1 milliohm.cm to 1 x 106 ohm.cm. Measurements outside of this range may be possible but will depend on sample type e.g. whether the sample is a thin layer or a volume sample.