What is the function of the altimeter in an aircraft?

The altimeter in an aircraft specifically serves the function of displaying altitude above sea level. It is an essential instrument in aviation that allows pilots to maintain proper altitude during flight, ensuring safe navigation and compliance with air traffic control instructions. The altimeter measures changes in atmospheric pressure, which decreases as altitude increases. By interpreting this pressure data, the altimeter provides a gauge of how high the aircraft is flying relative to sea level, which is critical for avoiding obstacles, adhering to altitude regulations, and ensuring a safe flight path. This capability is vital for both takeoff and landing phases, where precision in altitude is crucial for safety.