QFF

QFF is a Q code. It is the MSL pressure derived from local meteorological station conditions in accordance with meteorological practice. This is the altimeter setting that is intended to produce correct altitude indication (i.e., no error) on an altimeter at the actual sea level elevation, while QNH is intended to have no error at the station elevation (or, especially when applied within a region with a relatively small range of surface elevations, at the altitudes close to the surface elevation within the region).

Meteorological practice of calculating QFF differs between meteorological organizations around the world. Some examples: