Velocity ellipses in the meridional plane. The ellipses are colour-coded by their misalignment with respect to spherical alignment. The orientation that corresponds to spherical alignment is indicated by the dotted grey line through each ellipse. The inset in the top right of the figure shows the velocity ellipse for a non-tilted distribution with dispersions σ(v_R)=100 km s⁻¹ and σ(v_z)=50 km s⁻¹ (see Sect. 4 for more information). The contours show the (relatively small) formal statistical errors on the recovered tilt angles and are drawn for error levels of [0.5, 1.0, 2.0, 4.0] degrees. See Sect. 5 for a discussion on the effect of systematic errors.