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ship
anemometer and wind vane (photo KNMI)
Ships fitted with cup anemometers, wind vanes or anemographs, should report the mean reading over a ten-minute period or, if the wind changes markedly in the ten-minute period, an average over the period after the change. When observations are taken from a moving ship, it is necessary to distinguish between the apparent wind (NO allowance made for ship's course and speed) and the true wind (with respect to True North direction; allowance made for ship's course and speed). For the meteorological observation the true wind shall be reported. With this program the apparent wind will be converted to true wind automatically.
NOTE (ships only)

- If the apparent wind direction is used as input: please insert the apparent measured wind direction as accurate as possible. The computed true wind will be more accurate (e.g. insert 346 instead of the rounded value 350).

fixed sea station (rig, platform)
Fixed sea stations fitted with cup anemometers, wind vanes or anemographs, should report the mean reading over a ten-minute period or, if the wind changes markedly in the ten-minute period, an average over the period after the change