The 1120 ER is a professional instrument. The instrument is suitable for the testing of single earth electrodes such as lightning conductors and other small earthing systems. The resistance of conductors such as continuuity and condcuit coupling joints can also be measured. two terminal operation measurement, which reduces the accuracy, can also be done by shorting P and C terminals. The 1120 Er makes measurements by passing a conatant current through the device under test and measuring the voltage across it, The earth resistance is then calculated by Ohm's Law