The MD and MI are series of portable megohmmeters from Circutor which measure insulating resistances with values of TΩ and the use of a test voltage which can be selected by the user. the device offers a technology that offers an intake of accurate measurements and easy reading of insulated low and medium voltage electrical systems, transformers, motors, cables, equipment and home installations, distribution grids, and the like. The device is suitable for outdoor work and is capable of enduring tough usage conditions such as impacts and changes in temperatures. Its solid design also provides protection against intense vibrations during the transport on bumpy roads and sun ray resistance.