Thanks for replying guys....my unit is on a post that's about 2 metres high - exactly the same position as my last WH1900(?) which gave me no problems with wind speed (until it filled up with an ants' nest and stopped working!) During windy weather, it regularly reported speeds of 40 or so kph. My new WH2900 only reports 4 or 5 kph and the cups are spinning madly.
I adjusted the calibration which WAS on a factor of 50% (?!) up to 150%, but even now, it only reports about 6 to 8 kph when I have evidence that at its location point, the wind speed is MUCH higher - around 45kph. My thoughts are faulty hardware.