QNH

QNH is the atmospheric pressure at the aerodrome reduced to mean sea level. Set it in the subscale and the altimeter reads altitude above sea level, so on the runway it shows the aerodrome elevation rather than zero.

In a METAR it is the last group of the main body: Q followed by four digits for hectopascals, as in Q1013, or A followed by four digits for hundredths of an inch of mercury, as in A2992. Europe and most of the world use the Q form; the United States and Canada use the A form. Both describe the same pressure — 1013 hPa and 2992 (29.92 inHg) are the same standard setting.

Two related settings are easy to confuse. QFE is referenced to the aerodrome itself, so the altimeter reads height above the field and shows zero on the runway; it is not reported in a METAR. The standard setting of 1013.25 hPa is used above the transition altitude, where readings become flight levels rather than altitudes. A METAR gives you QNH only — anything else has to be set from it or from ATC.