Assume 27 ft/hPa.
QNH. The atmospheric pressure adjusted to mean sea-level. If you are on the ground at an airport and turn in the local QNH at your altimeter’s subscale, it will display the airports altitude above sea level.
QFE. The pressure set on the altimeter so that it indicates the height above the reference elevation being used (height above current ground level).
In the case of this specific question: The question states that the QFE is 980 hPa, and that Locarno is 200 metres above sea level. They ask us to calculate the QNH.
Let's start by converting 200 m into ft. (1 metre is 3.28 feet)
3,28 x 200 = 656 feet
We now want to know how many hPa correspond to 656 feet, therefore we divide it by 27 (27 is the amount of feet per 1 hPa close to the ground) = 24.3 hPa
- QNH = 980 hPa + 24.3 hPa = 1004.3 hPa = 1005 hPa approx.
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Spain