[laulau]

Ok,
But if you take the line :
10 37.4
It gives 37.4/10/3.6 = 1.038 m/s

This mean that the anemometer form factor is not linear !
If I draw the curve, the factor is close to 1 from 10km / h and goes up to 2 for very low speed.

I haven't calculated it! It is in the table provided by Steve link.

...
For your anemometer, you may also need to know the wind speed correspondent to 1 click / revolution, and make the necessary changes in the software.

Code:

Revolutions vs. Wind Speed
Revs/sec Frequency    Airspeed km/h
    
1.0                       6.5

6.5 Km/h = 1.80 m/s (WeatherDuino Pro2 internally always use Internacional System Units)