What is used to measure altitude in aviation?

Altitude in aviation is primarily measured using a barometer. The reason for this is that a barometer measures atmospheric pressure, which decreases as altitude increases. By comparing the current atmospheric pressure at the aircraft's altitude to a standard pressure value at sea level, pilots can determine their altitude above sea level. This measurement is crucial for ensuring safe flight operations, navigation, and maintaining proper altitudes within controlled airspace.

While gyroscopes, compasses, and thermometers are important instruments in aviation, they serve different purposes. Gyroscopes provide information on aircraft orientation and stability; compasses help determine heading or direction; and thermometers measure temperature. Each instrument plays a distinct role in the cockpit but does not directly provide altitude information like a barometer does. Thus, the use of a barometer for altitude measurement is foundational in aviation.