What's appen with my analog pin

Apparently the problem come from my board. I tried with another one and I got some better result. I will not debug my board for now because something worry me about the Wind direction measure

The code is here and the schema here

I am oberserving the analog input. My analogReadResolution is now to 10.

The doc say, the wind direction read at A0 is from 0 to 1023.

0 and 1023 is noth.
I supposed the south is around 512.

When I move the van to 180°, then to the south, the read, at A0, 787 whch is West.
When I move the 90° (Est), I read 612
When I move the van close to 10°, I read 200 which is EST.

That's sound not good, isn't? If I move the van to 180°, I should read around 512.
What should be the reason?

Then I wonder, if I should forget that exemple and calibrate the noth,est,south,west following what I read at A0.