The Three-Terminal Ground Resistance Tester is the economical choice for electrical contractors, plant electricians, telephone and CATV technicians making routine ground resistance tests on single electrodes and other simple grounding systems. The instrument is easy to use for quick measurement of resistances from 0.5 to 500 ohms. Because factors such as seasonal variations in temperature, moisture and salt content affect soil resistivity, periodic tests are essential to ensure that resistance to ground remains at a safe value.