oi vey...
There are the ICAO and WMO standards.
METAR Wind Velocity
Wind velocity in a METAR is stated as the measured or estimated mean of each component over the 10 minutes prior to the time of issue of the METAR, unless there are significant variations during this 10 minute period. For direction, this means 60 degrees or more of arc but less than 180 degrees provided that the mean speed during the previous 10 minutes has been more than 3 knots. In the case of speed, variations from the mean wind speed (both above and below it) are reported when the variation from the mean speed has exceeded 10 kts. Such variations are expressed as the maximum and minimum speeds attained and must also be included if the maximum wind speed in a 10 minute period has exceeded the 2 minute average wind speed at the same location in that period. Any gust value which has occurred in the most recent two minute period will of course also be part of the calculation of average wind speed
Wind direction is recorded in degrees true. Whatever runway(s) is (are) in use, the wind velocity for the METAR is normally taken from one designated anemometer.
ATIS Wind Velocity
ATIS wind velocity is latest two minute average.
The wind direction broadcast is given in degrees true. The mean wind speed is supplemented by the value of the highest and lowest gusts within the 10 minutes prior to issue time if either exceeds the METAR-specified minimum difference increment away from the mean.
ATIS broadcasts are usually only updated between the regular change times if the wind direction changes by more than 30 degrees or the 2 minute average wind speed changes by more than 5 kts over a five minute interval.
ATC Wind Velocity Reports
Display of wind velocity information to ATC at major airports usually allows at least the reporting by RTF of both the ‘average wind’ - that over a two minute period updated every minute - and ‘instant wind’ - the value at that exact time. The latter is usually used only where high wind speeds and their associated greater fluctuations in speed and direction prevail. ATC may pro-actively initiate such ‘wind checks’ or this action may be requested by a flight crew. The ATC TWR at most international and major domestic airports have digital displays of wind velocity which can be specific to sensor site or integrated from several sites and can show a selection of trend and extremes data. Smaller airports may still be limited to dual and plotted graphical displays from which to derive both required broadcast information and additional ad hoc assistance.
ATC plain language ad hoc wind directions given during final approach or just prior to or during the take off roll are likely to be given in degrees magnetic.
Search through AIP for "magnetic".
Which AIP?
On a side note, what do your FMS and IRS winds use?
EDIT: Sorry that was a trick question. The FMS and IRS use the digital winds calculated in true. The ND winds are shown in mag. There is always a comparison going on between the input winds and the actual.
