What is the purpose of the altimeter setting?

The purpose of the altimeter setting is to calibrate the altimeter to the local atmospheric pressure so that it accurately reflects the aircraft's altitude above sea level. The altimeter measures altitude based on the principle that atmospheric pressure decreases with an increase in elevation. By setting the altimeter to the current barometric pressure at sea level, pilots can ensure that the readings reflect true altitude rather than being affected by changing weather conditions. This calibration is essential for safe navigation, particularly when flying at lower altitudes where terrain and obstacles are present. Accurate altitude readings are critical for maintaining proper separation between aircraft, avoiding terrain, and ensuring compliance with air traffic control instructions.