Which statement best describes the purpose of an altimeter?

The purpose of an altimeter is to measure and display altitude based on atmospheric pressure. An altimeter works by sensing changes in air pressure as an aircraft ascends or descends. The atmospheric pressure decreases with an increase in altitude, and by converting the measured pressure into altitude readings, the altimeter provides pilots with crucial information about their current elevation above sea level or the terrain below. This function is essential for safe navigation, compliance with air traffic control instructions, and avoiding obstacles during flight.

The other options do not accurately reflect the function of an altimeter. Calculating fuel load pertains to fuel management systems, engine performance assessment involves monitoring engine parameters and efficiency, and tracking flight speed is associated with airspeed indicators. Thus, the correct answer underscores the specific role an altimeter plays in aviation.