The four point electrical probe is a very versatile device used widely in physics for the investigation of electrical phenomena The effects of contact resistance can be eliminated with the use of a four point probe. A constant current is made to flow the length of the sample through probes labeled 1 and 4 in the figure. This can be done using a current source or a power supply as shown. Many power supplies have a current output readout built into them. If not, an ammeter in series with this circuit can be used to obtain the value of the current. A 5 Watt power supply capable of producing up to 0.5 Amp is required for the experiments described for our superconducting devices.