What is the purpose of the altimeter?

The primary purpose of an altimeter is to measure the aircraft's altitude above sea level. It provides crucial information to pilots, allowing them to maintain a safe altitude and comply with airspace regulations. The altimeter measures atmospheric pressure changes as altitude changes; higher altitudes correspond to lower pressure. By utilizing this relationship, the altimeter can be calibrated to indicate the altitude at which the aircraft is flying.

Other functions, such as measuring airspeed, indicating the rate of climb, or displaying the orientation of the aircraft, are performed by different instruments in the cockpit. For example, a pitot tube is used for measuring airspeed, a vertical speed indicator shows the rate of climb or descent, and an artificial horizon or attitude indicator displays the aircraft's orientation relative to the horizon. Thus, the altimeter's specific and essential role is in altitude measurement, distinct from the functionalities of these other instruments.