A precision instrument suitable for calibrating and testing general purpose insulation testers and megohmmeters with test voltages up to 10kV. It is constructed in a high strength co-polymer plastic case and is powered by a rechargeable battery. This ensures full isolation from the mains and prevents stray leakage.The insulation tester being calibrated can be tested for open circuit voltage and short circuit current. These are displayed on the digital meter mounted on the front panel. The insulation resistance is provided by a precision 4 dial decade resistance bank which can be set to a maximum of 99.99GΩ with additional resistance values of 100kΩ, 200kΩ, 500kΩ, 1MΩ, 2MΩ and 5MΩ which can be switched in as required.