ICAO Doc 8896 - "Manual For Aeronauticac Meteo Practice"
2.3.7.2 Direction (true) from which surface wind is blowing should be indicated in degrees rounded off to the
nearest 10°. The unit used for wind speed should be indicated both in local routine reports and METAR. In local routine
reports, the term “CALM” is used when a wind speed of less than 0.5 m/s (1 kt) is observed. Wind speed of 50 m/s
(100 kt) or more is to be indicated as ABV49MPS or ABV99KT.
Note 1.— Wind direction reported to aircraft for landing or take-off purposes must be converted into degrees
magnetic. This conversion is normally carried out by the ATS unit concerned.
Infatti il tower wind è magnetico, così come l'ATIS. Il resto è true.
Ogni volta che ricevo i bollettini di Gander, Norfolk ecc, mi faccio un mazzo tanto a capire quale pista posso usare visto che 20gradi di var fanno una bella differenza.