'Digitherm' digital electronic thermometer with probe, c 1970s.
© Science Museum / Science & Society Picture Library
Thermocouple thermometer based on the Seebeck effect (thermoelectricity). One junction of the thermocouple is at the tip of the probe - the thermocouple produces a voltage which depends on the difference between the temperature of this junction and the room temperature. Circuitry in the display unit converts the voltage to a temperature difference, compensates for room temperature, and displays the result as a digital reading. It measures temperatures from minus 50 to plus 999 degrees celsius.