What instrument is used to measure altitude?

The altimeter is the instrument specifically designed to measure altitude. It operates by determining the atmospheric pressure surrounding the aircraft, which decreases as altitude increases. The altimeter is calibrated to a standard pressure level, allowing pilots to gauge their elevation above sea level accurately.

When a pilot adjusts the altimeter setting to the current local pressure, they ensure that the altitude reading reflects the actual height above the terrain. This instrument is crucial for safe navigation, as it helps pilots maintain the correct flight level, avoid terrain, and comply with air traffic control instructions.

In contrast, the airspeed indicator measures the speed of the aircraft relative to the surrounding air, the attitude indicator shows the orientation of the aircraft in relation to the horizon (indicating whether the wings are level, climbing, or descending), and the vertical speed indicator provides the rate of climb or descent in feet per minute. None of these instruments serve the purpose of measuring altitude directly, which is the primary function of the altimeter.