The outside air temperature (OAT) gauge is a simple and effective device mounted so that the sensing element is exposed to the outside air.
The sensing element consists of a bimetallic-type thermometer in which two dissimilar materials are welded together into a single strip and twisted into a helix. One end is anchored inside a protective tube, and the other end is affixed to the pointer, which reads against the calibration on a circular face.
OAT gauges are calibrated in degrees Celsius (°C), Fahrenheit (°F), or both. An accurate outside air temperature provides the pilot with useful information about the temperature lapse rate with changes in altitude. [Figure 1]
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| Figure 1. Outside air temperature (OAT) gauge |