Selection of the correct sign of the asf for the MC observed on 22 August 1995. The MC region is shown with a blue background. (a) The magnetic field magnitude. (b), (c), (d) The magnetic field components, normalised to the field magnitude, in the FR frame. Two Lundquist solutions fitted to the observed magnetic field components, with their origin set at t_0, minus (blue) and t_0, plus (red) is added in (b), (c), (d). (e) The observed velocity profile. The correct sign of the asf is determined by the best fit represented by the lower χ_R value (Eq. (8)). Here it is for sgn(asf)=1 (red curves).