How do you adjust the altimeter setting in a Cessna 172?

The altimeter setting in a Cessna 172 is adjusted using the Kollsman window, which is an essential feature of the altimeter instrument. The Kollsman window allows the pilot to set the current local atmospheric pressure, usually provided in inches of mercury (inHg) or millibars (hPa). This adjustment ensures that the altimeter displays an accurate altitude relative to sea level.

When pilots set the altimeter to the correct local pressure, they are calibrating their altitude readings based on current weather conditions. This is crucial as atmospheric pressure can change due to weather systems, affecting altitude measurements. By properly setting the Kollsman window, pilots can ensure they maintain safe altitudinal separation from terrain and other aircraft.

Adjusting the altimeter based on aircraft weight or cabin pressure is not applicable in the context of a Cessna 172, as altitude notice is strictly a function of atmospheric pressure, not influenced by aircraft weight. Similarly, the altimeter does not require resetting every hour; it should be adjusted whenever entering a new area with a different local pressure setting or upon receiving updated weather information.