Anemometer readings are wrong

Hi,

I added the anemometer to my weather station a couple of days ago, and I notice that the readings are far from correct.

Right now it says 3.1 m/s whereas the official reading from the Danish Meteorological Institute at the airport just 3  km from here says 6.3 m/s. That's more than double up compared with Netatmo's reading.

The anemometer is placed 1.5 m above the chimney in a total height of 8-10 m. I have tried to calibrate the sensor by entering 8 m in the app, but it doesn't change much.

Is the anemometer broken or is it just the accuracy I can expect from this device?

Thanks!