Pitch angle of each spiral, in the non-deprojected (top) and deprojected image (bottom). For each measurement, we considered either the whole trace (for S1, features i and ii), or consecutive arcs subtending 50^° (for S2 and S3) to trace the evolution of the pitch angle along the trace in order to provide reliable pitch angle estimates. The estimate for feature ii has a larger uncertainty because its trace only subtends ~ 25^°, instead of ~ 50^° for S1 and feature ii.