Comparison of the inverse of the observed brightness times a fitted scaling factor f(v₀) (red vertical bars) and the theoretical Jacobian J(t − t₀,v₀) (black dashed curve) as a function of time after jet initiation at t₀. is a reference time at 04:46 UT. The different diagrams are obtained for different initial velocities v₀, which lead to different particle orbits along which is recorded. The vertical range of the red bars indicates the estimated error in B. The width between the two solid black curves on both sides of the dased curve shows the variation of J due to an uncertainty in t₀. For more details see text.