Twist per unit length (converted into a unit-less quantity ) of magnetic field lines starting at the x-axis inside a toroidal flux rope (x in the plot is the starting point). The red line is for R₀/r₀ = 5 and the first-order solution, the blue line for R₀/r₀ = 5 and the zero-order solution, the green line for R₀/r₀ = 3 and the first-order solution, and the magenta line for R₀/r₀ = 5 and the MT field. It is br₀ = 1.5. This value is shown by the dashed horizontal line. The plot for the uniform-twist flux rope would coincide with this dashed line.