What is the purpose of the altimeter setting?

The purpose of the altimeter setting is to adjust the altimeter to local atmospheric pressure, ensuring that altitude readings are accurate. The altimeter is an instrument that measures altitude by comparing the pressure of the surrounding air to a reference pressure. Atmospheric pressure changes with weather conditions, so pilots must set their altimeters to the current pressure at sea level, known as the altimeter setting.

When the local atmospheric pressure is accurately set, the altimeter will display the correct altitude above sea level. This is crucial for maintaining safe altitude separation from other aircraft and terrain, especially during takeoff, landing, and when flying in controlled airspace. By using the local altimeter setting, pilots can ensure they are aware of their true altitude in relation to the ground and other aircraft, which is vital for aviation safety.