The MEGGER® DET3/2 Digital Earth Tester is a compact instrument designed to measure earth electrode resistance and soil resistivity. The instrument uses the four-terminal method of measurement, in which the resistance of the current circuit does not affect the reading. The instrument circuit has been designed so the resistance of the potential circuit also does not affect the measurement. Pressing a latchable button converts the instrument from its four-terminal measurement mode to a three-terminal one. The reversing DC test current has a frequency of 128 Hz, which avoids possible interference from other 50 and 60 Hz stray currents in the vicinity of the earth electrode under test. In the interests of safety, the maximum test voltage has been limited to 50 V.