Method of determining a position of a sensor device relative to a magnetic source, includes: a) determining a first and a second magnetic field component at a first sensor location; b) determining a third and a fourth magnetic field component at a second sensor location; c) determining a first difference of the first and third component, and determining a second difference of the second and fourth component, and determining a first angle based on a ratio of the first and second difference; d) determining a first sum of the first and third component, and determining a second sum of the second and fourth component; e) determining a second angle based on a ratio of said first and second sum; f) comparing the first and second angle to detect error.