Hi Christofer Smith,
What part of the world are you trying to map and do you know what the magnetic declination should be for that area? This could rule out the chance of it falling on an Agonic line where the declination is zero. I notice with the Magnetic arrow you set the calibration. If you add in the topographic north arrow does it have the same issue with 0 Grid - Magnetic variance? Hopefully this helps answers your question.
Shane