What is the Kollsman window used for in aviation instruments?

• A. To adjust the heading indicator using compass deviation
• B. To set the altimeter pressure setting
• C. To calibrate the airspeed indicator
• D. To measure the magnetic variation

Answer: (B)

The Kollsman window on the altimeter is used to set the al timeter pressure setting. It lets you dial in the local reference pressure (the altimeter setting, such as the local QNH) or, when flying at higher altitudes, the standard pressure (29.92 inHg or 1013 hPa) for flight levels. By adjusting this setting, the altimeter reads your true altitude relative to mean sea level as the atmospheric pressure changes. If you don’t set the correct local pressure, the instrument will indicate the wrong altitude because it assumes the entered pressure is the standard reference. This window is specific to the altimeter; heading indicators, airspeed indicators, and magnetic variation are derived from other instruments or sensors and aren’t adjusted with the Kollsman window.