turns out that the premise of using this chip alone as a compass is basically flawed. it can't do its own tilt compensation because the earths magnetic field is not necessarily parallel to the earth .
as George says an accelerometer needs to be added to compensate for tilt. (read, complicated math probably needs floats for any decent accuracy)

no wonder they are so cheap , not a total loss it makes a pretty sensitive 3 axis hall effect sensor , nice colour