Board is not upside down, arrows on top pointing right, but I had to turn orientation as described to meke the flight data showing OK...
I know that from the documentation it was supposed to be -90deg. But if I put that, flight data is inverted and quad flip (I try it) As another test I turn my fc with the arrow pointing front (see picture) in flight data now the roll is inverted. I don't understand ... ...
When looking at Flight Data page and you roll left THE HORIZON rolls right, and that is normal.