MIL-T-19646A, MILITARY SPECIFICATION: THERMOMETER, GAS ACTUATED, REMOTE READING (08 FEB 1990)., This specification covers environmentally hardened thermometers which utilize an elastic element to measure the pressure within a gas filled closed system (thermal system) and convert this pressure to an analog temperature indication on a circular dial. Remote reading is accomplished by connecting the analog temperature indicator to the thermometer bulb by a specified length of capillary tubing. The gas actuated thermometer bulb is configured for either direct immersion or insertion into a thermowell.