This SAE Aerospace Standard (AS) covers two basic types of temperature instruments as follows: Type I: Ratiometer type, actuated by changes in electrical resistance of a temperature sensing electrical resistance element; the resistance changes being obtained by temperature changes of the temperature sensing resistance element. Type II: Millivoltmeter type, operated and actuated by varying EMF output of a thermocouple; the varying EMF input to the instrument being obtained by temperature changes of the temperature sensing thermocouple.