Same as Fig. 2, but with an external magnetic field B. The precession of the grain is now with respect to the orientation of В with a precession angel of ϕ. Note that the angle ψ between the gas-dust drift Δs and В as well as the magnitude of В are free parameters in this model. In this configuration the resulting angle of alignment ξ is between В and â₁ whereas the angles Θ and Φ may be expressed now as functions of ξ and ψ.