Value of Δ as a function of b_GH of the Gold-Hoyle tube which fits a core-envelope flux rope, the parameters of which are kept constant. Δ characterizes deviations of the two field profiles scaled by their field-magnitude maxima, and it corresponds to the quantity χ used when real observations of magnetic clouds are compared to models (e.g., Lepping et al. 2006). Results for three sets of parameters of the core-envelope model, shown at the top, are plotted and indicated by color. Panel a is for a central crossing, while panel b is for a crossing in a distance of 0.2 r₀ from the magnetic axis.