An extra pair of leads that are used in conjunction with a sensitive measuring instrument connected to a bridge circuit. The leads are identical to those that connect the measuring device, such as a resistance thermometer, to the bridge and run alongside them. They are shorted at the instrument end and connected in series with the balancing element of the bridge circuit. Any resistance in the working leads is thus balanced by the compensating leads and resistance changes that occur in the working leads due to ambient conditions are also produced in the compensating leads.