Schematical explanation of the geometrical parameters in the special case when the precession axis of the disk (the symmetry axis of the conical surface over which the rotation axis of the disk moves cyclically with the precession period P_prec) is parallel to the Y axis of the coordinate system (i.e. it is perpendicular to the orbital plane). Our code allows this axis to be inclined by angles θ_prec and φ_prec in a similar way to the inclination of the rotation axis.