The Edgetech Instruments Model 137 Vigilant Aircraft Hygrometer is a rugged, shock mounted military qualified instrument used for the primary measurement of dewpoint in flight or in installations with existing flow, such as wind tunnels. It features a miniature remote dewpoint sensor employing a platinum resistance thermometer, and has 15 feet of interconnecting cable to the control unit. Precision calibration units for the linear analog outputs are included. The specially designed dewpoint sensor is mounted through the skin of the aircraft and is mounted to either the left or right side of the aircraft. The dewpoint is detected by using chill mirror technology assuring precision accuracy, repeatability and reliability.