the resistances of resistors arranged in a matrix form in a pressure - sensitive resistor mat are measured with high accuracy and using simple circuitry by the fact that the output of an operational amplifier is connected to each row conductor and each column conductor , which are connected to the resistor . a voltage is selectively applied to the individual resistors by appropriately activating the operational amplifiers . each operational amplifier associated with the row or column conductors is equipped with a current balancing circuit which detects the output current of the operational amplifier connected to the selected resistor which flows through this resistor . a processor determines the individual resistance values from the currents flowing through the individual resistors and the voltage drops across those resistors .