Altimeter setting is the value of the atmospheric pressure used to adjust the sub-scale of a pressure altimeter so that it indicates the height of an aircraft above a known reference surface. This reference can be the mean sea level pressure (QNH); the pressure at the nearby surface airport (QFE); or the pressure level of 1,013.25 hectopascals (29.92 inches of mercury) which gives pressure altitude and is used to maintain one of the standard flight levels. The setting of a sensitive pressure altimeter is shown in the Kollsman window.