This is normal when the compass is not calibrated. To calibrate, you have just to go sailing. If you want to calibrate at home you have to simulate boat movement and change heading slowly until complete 60 degrees minimum. Sometimes the metallic structure of your building is enough to not calibrate successfully and the best test is the real life.
See the docs for more info: https://docs.sailoog.com/openplotter-v1-...alibration
See the docs for more info: https://docs.sailoog.com/openplotter-v1-...alibration