why #insulation tester should be #calibrated? An insulation tester (also called a megohmmeter or “megger”) should be calibrated because it is a precision electrical measuring instrument used to assess insulation resistance in cables, motors, transformers, and other electrical equipment. Here’s why calibration is important: 1. Accuracy of Measurements Insulation resistance values are often very high (in the megaohm or gigaohm range). Small errors in measurement can lead to false conclusions about