Average of the line-of-sight component of the magnetic field as a function of the linear distance to the centre of the nebula. The curve shows the result of the reference fit, for which B₀ = 7 μG, θ₀ = 25°, and B_{0 | |} = 6.3 μG, as indicated by the horizontal dashed line. The three vertical lines delineate the inner and outer radii of the H ii region and the outer radius of the dust shell:  pc;  pc; and  pc.