Abstract: The invention employs a pair of known resistors which are permanently connected to the input terminals to which the unknown resistor may be connected. A source of d.c. voltage is connected to one input terminal and the voltage drops produced across each known resistor are alternately sampled and supplied to an A/D converter which converts these voltage drops into corresponding digital signals. A microprocessor computes the quantity VR1/VR2-1 where VR1 is the voltage drop across one known resistor and VR2 is the voltage drop across the other known resistor. The computed quantity is a linear function of the value of the unknown resistance. This computed quantity may then be converted to a corresponding analog signal and supplied to a meter. Since no switches are connected across the unknown resistor, leakage problems normally associated with extremely high resistance measurements are virtually eliminated and very high resistances in the order of 5000-10,000 megohms may be accurately measured and displayed.