Orientation of the best plane (X^′,Y^′) that minimizes the velocity component (V_Z′) of the CH₃OH masers perpendicular to the plane. Upper panel: left and right plots show a view of the best plane as projected on the plane of the sky and with respect to the line of sight, respectively. Lower panel: ratio of the velocity components perpendicular (V_Z′) and parallel (V_p) to the best plane, plotted for each maser cloudlet (grouped by clusters). Error bars give the 1σ uncertainty of the ratio V_Z′/V_p. The dotted line marks the weighted average of V_Z′/V_p (with its uncertainty), which corresponds to an average deviation of 12° away from the best plane.