Using a fine wire type N thermocouple as the surface temperature sensor, the Isotech Model 944 pairs that with a second junction 2 to 3mm along the thermocouple and senses the temperature difference due to heat flux along the sensor. A heater heats the thermocouple stem until the temperature gradient is zero, thus creating a measurement without stem conduction or disturbance of the hot plate's surface.

The Isotech Model 944 surface measurement system indicates true surface temperature between 30 an 350°C with a ±1°C stability. The resolution of the display can be set for either 0.1°C or 0.1°F. This unit, when supplied with a traceable calibration certificate, offers an accuracy of ±2°C (±5°C without). The included semi-standard thermocouple measures 7.5mm in diameter, 150mm long and 850 lead length.