Magnetic field components versus time (in hour) in the FR frame (black), in the MV0 frame (orange, MV using B) and in the MV1 frame (green, MV using ). The various components are compared in the same graphs. All panels are for a static (ζ = 0) Lundquist’s FR (b/a = 1). A relatively large impact parameter, p = −0.5, is selected to show the differences (p <  0 then B_x >  0 for this FR with positive magnetic helicity). Panel a shows B and panel b shows . The other parameters are B₀ = 1 at t = 0, V_c = 400 km s⁻¹, b₀ = 0.1 AU.