What happens to the altimeter reading when altitude increases from high to low?

When flying from a high altitude to a low altitude, the altimeter reading decreases. This is because an altimeter is designed to measure atmospheric pressure, and as altitude decreases, atmospheric pressure increases. The altimeter is calibrated to show the altitude based on the standard atmospheric pressure at sea level. When you descend, the pressure sensed by the altimeter is higher than it was at the higher altitude, leading to a decrease in the reading on the altimeter.

Understanding this principle is critical for pilots, as they must continuously monitor altitude to maintain safe flight operations, especially when approaching an airport or flying in controlled airspace. Adhering to altitude readings ensures safety in navigation and prevents potential collisions with terrain or other aircraft.