High resistance decade box is aimed for calibrating of insulation meters and megaohm-meters. It is suitable for calibration laboratories and service centres, where can be used also for testing or setting of high resistance meters. High voltage relays with extremely high insulation resistance are used for switching of resistance components. M-109R is equipped with indication of input terminal overload. Instrument is supplied from internal accumulator or power line adapter. Control is possible manually or remotely via serial interface RS-232.