What does an altimeter measure?

An altimeter measures the height of an aircraft above sea level, which is crucial for navigation and safety. It uses atmospheric pressure to determine altitude; as an aircraft ascends, the air pressure decreases, and the altimeter reflects this change in pressure to provide an altitude reading.

This measurement is essential for pilots as it helps them maintain a proper flight level, adhere to air traffic control instructions, and ensure safe separation from terrain and other aircraft. Knowing the altitude is vital for various phases of flight, including takeoff, cruising, and landing, contributing directly to the overall safety and efficiency of flight operations.

The other options, while relevant to aviation, do not pertain to what an altimeter measures. For instance, speed is gauged by a separate instrument called an airspeed indicator, weight is monitored using load management systems, and cabin temperature is measured by environmental control systems.