Ground resistance meter 3-electrode measurement on the 3151 gives greater precision! Ground resistance measurement involves factors that are not encountered during ordinary resistance measurement, such as polarization of the earth, the influence of grounding current due to leak current and grounding voltage, and the influence of auxiliary grounding resistance. The 3151 is able to make more accurate measurements more safely under difficult conditions because it uses the alternating current potentiometer method to provide measurement accuracy, and because it contains features such as an auxiliary grounding resistance check feature and measurement frequency switching.