What atmospheric condition is measured by the altimeter setting?

The altimeter setting is a crucial measurement in aviation, specifically associated with atmospheric pressure. It reflects the local air pressure adjusted to sea level, which is pivotal for determining an aircraft's altitude. When pilots set their altimeters before flight or during approach and landing, they rely on this setting to ensure accurate altitude readings. The altimeter utilizes the principle that air pressure decreases with an increase in altitude; thus, monitoring this pressure allows for precise spatial awareness in the three-dimensional environment of the atmosphere.

In aviation, atmospheric pressure varies based on weather systems, temperature changes, and altitude, making the altimeter setting essential for flight safety and navigation.