The magnetic pitch angles in M 101 at λ 6.2 cm shown in greyscale with apparent B-vectors and some contours of the H i   spiral arms (Braun 1995) superimposed, smoothed to the beamwidth of . The contour levels are (10, 15, 20, and 25) 10²⁰ cm^-2. The pitch angles are corrected for the inclination of 30°, but not for Faraday rotation because it is <7°. The pitch angles are smallest in the south-west, where the apparent B-vectors run nearly parallel to the H i  arms, but pitch angles near −40° occur in the south and the north. The length of the B-vectors is proportional to the non-thermal degree of polarization with 1′ = 20%.