Plane-of-sky GMF unit vectors over the Perseus molecular cloud showing the coherent GMF model obtained from the Hammurabi code. The background gray-scale image shows the extinction map from Kainulainen et al. (2009). The red vectors show the GMF unit vectors in the plane of the sky. Left panel: Cyan line represents the approximate filament axis, with B_‖ directions reversing in the direction perpendicular to this axis. Right panel: for the ease of comparison with Fig. 5, the Perseus cloud and GMF vectors are shown in galactic coordinates.