What calibrated instrument (or weather
station) are you comparing your readings to? And as stated by another poster in this thread, what height is the reference data coming from as compared to your instrument's height?
Is your unit reading high when under sail, & of so on what points of sail? Or is it always reading high, both when sailing & not?
How far in front of, & or above your masthead is the sensor on the wand?
Also, calibrating it is a lot more complex & involved than just setting it while driving around in a circle. Though how well you want it to be calibrated is going to determine how much work
goes into the calibration process. Which can get quite complex if you want it to be very close to perfect under most conditions & points of sail.