What instrument is typically used to indicate altitude?

The instrument that is commonly used to indicate altitude is the altimeter. This device measures the aircraft's altitude above a reference level, usually sea level, by comparing the atmospheric pressure outside the aircraft to a pre-determined value. As an aircraft climbs or descends, changes in air pressure occur, which the altimeter uses to provide an accurate reading of altitude.

The altimeter is calibrated to understand how pressure decreases with an increase in altitude; therefore, it gives pilots crucial information about their relative elevation during flight. This makes it essential for safe navigation, especially when flying in controlled airspace or as part of instrument flight rules (IFR).

In contrast, other instruments serve different functions. The variometer is primarily used to indicate rate of climb or descent rather than the actual altitude. The airspeed indicator measures the speed of the aircraft relative to the airflow around it, while the compass provides directional guidance. Each of these instruments plays a vital role in aviation, but the altimeter stands out as the definitive instrument for indicating altitude.