A thermocouple circuit is, as shown in Fig. 7.1, by its nature a differential measuring device, producing an emf which is a function of the temperatures of its two junctions. One of these junctions is at the temperature which is to be measured and is referred to as the measuring junction. The other junctions are at a known temperature and are referred to as the reference junction. (In a practical thermocouple circuit (see Section 2.3) copper wires are often connected to the thermocouple alloy conductors at the reference junction. The term reference junctions will be used to refer to this situation.) If these junctions are both at the same temperature, the presence of the copper “intermediate metal” introduces no change in the thermocouple's emf [1]. Refer to Sections 2.4 for a discussion of this theory.