Consider the measurement of temperature of a heated surface as shown in Figure 2.14. Wheatstone bridge is commonly used for direct measurement of wire resistance, as shown in Figure 2.15 where is the DC power source with a stability of better than 1 mV, is a galvanometer used to check for null current, , are control resistors that reduce the current level in the circuit and , are the lead and wire resistances, respectively. The presence of in the parallel arm of the bridge compensates for temperature gradients that will exist in the lead wires. When the bridge is balanced