This Aeronautical Standard covers two basic types of temperature indicators as follows: TYPE I - Ratiometer type actuated by changes of 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 e.m.f. output of a thermocouple, the varying e.m.f. input to the instrument being obtained by temperature changes of the temperature sensing thermocouple.