A measurement principle is explained to accurately scan magnetic fields even if the fields are strongly inhomogeneous as in automotive applications. To measure the misalignment, the idea is scanning a part where the geometry is exactly known and comparing the measurement results with the ideal geometry. A sphere is chosen as reference geometry because accurate reference spheres are commercially available, and a sphere does not have to be aligned in the measurement setup. Another approach is measuring the misalignment of the optical probe and compensating for it mathematically or mechanically. After a calibration of the setup, the magnetic field can be measured in the coordinate system of the field source so that assembly tolerances do not impair the measurement. The idea of calibration is using an inhomogeneous reference field source that has a strong relation between its magnetic field and its geometry.