a)  Orientations of the apparent B-vectors (plotted with equal length) in M 101 at λ 6.2 cm (corrected for inclination) in the frame of azimuthal angle in the disk plane and ln(r) (r is the galacto- centric radius in arcmin), overlaid onto the H i  distribution of Braun (1995), smoothed to a beamwidth of 20′′. b)  Orientation of the B-vectors (plotted with equal length) of the magnetic field model assuming the magnetic field to be parallel to the H i   filaments. Ellipses show the beamwidth at selected radii. c)  Differences between model and observations shown as symbols with size proportional to the pitch angle difference (the scale is given at the top of the figure). As the pitch angles are mostly negative, a negative difference means a more inclined B-vector in the observed than in the model map. The azimuthal angle runs counter clockwise from the NE major axis.