What does an altimeter measure?

An altimeter measures altitude in relation to mean sea level by detecting changes in atmospheric pressure. The principle behind its operation is based on the fact that atmospheric pressure decreases as altitude increases. Thus, when a pilot sets the altimeter to a local pressure setting, the device can accurately calculate the height above sea level based on the ambient air pressure. This is crucial for navigation and ensuring safe flight altitudes, as maintaining the correct altitude is essential for avoiding terrain and other aircraft.

While atmospheric pressure is the underlying factor that allows an altimeter to function, the primary output is a specific altitude reading, typically indicated in feet or meters above mean sea level. Understanding this measurement is paramount for pilots in order to comply with altitude regulations and safely navigate various airspace conditions.