Which instrument displays the altitude of an aircraft?

The instrument that displays the altitude of an aircraft is the altimeter. This device measures the aircraft's altitude by comparing the atmospheric pressure outside the aircraft to a pre-measured standard atmospheric pressure, typically at sea level. As the aircraft climbs or descends, the change in external pressure is registered, allowing the altimeter to provide a readout of the altitude in feet or meters.

While the speed indicator measures the aircraft's speed, the vertical speed indicator provides the rate of climb or descent, and the heading indicator shows the direction in which the aircraft is flying, it is the altimeter that specifically indicates how high the aircraft is flying above sea level or the terrain beneath it. Therefore, the altimeter is essential for safe navigation and altitude management in aviation.