What does the altimeter measure in aviation?

The altimeter is an instrument used in aviation to measure altitude. It specifically operates based on the atmospheric pressure, providing readings in inches of mercury (inHg) or millibars (hPa). As an aircraft ascends or descends, the surrounding atmospheric pressure changes, and the altimeter adjusts its reading accordingly to indicate the aircraft's altitude above sea level.

Altitude measurement is critical for safe flight operations, as it helps pilots maintain the necessary vertical separation between aircraft and adhere to air traffic control instructions. Understanding altitude is vital for navigation and preventing collisions.

In contrast, temperature measurements, distance in nautical miles, or heading in degrees relate to other instruments and are not functions of the altimeter. Temperature is measured by a thermometer, distances might be calculated using GPS or other navigation systems, and heading is provided by a magnetic or gyro compass. Thus, the unique function of the altimeter is to provide altitude readings in inches of mercury.