Abstract: Apparatus is disclosed which provides an improved means of measuring the operating characteristics of a multiplicity of thermocouple reference junctions. The apparatus allows accurate sensing of temperature through use of both a measurement and reference junction thermocouple arrangement. The reference junction thermocouples are collectively encased and surrounded by an insulating medium which on one side abuts a metal plate serving as a heat sink of appreciable mass. The operating temperature of the heat sink is then monitored by a temperature sensitive resistor. Voltage drop across the resistor is convertible into a measure of system calibration.