Earth testers, also known as ground resistance testers, are essential instruments used to measure the resistance of grounding systems. Proper grounding is crucial for safety and the effective functioning of electrical systems. Calibration of earth testers ensures their accuracy and reliability, which is vital for maintaining electrical safety standards. What is an Earth Tester? An earth tester, also known as a ground resistance tester, is a device used to measure the resistance of the earth grounding systems. Grounding is essential for electrical safety, ensuring that fault currents have a path to the ground, reducing the risk of electric shock, and preventing equipment damage.