Comparison of the azimuthal velocity distributions v_ϕ for stars in the bin 9 < R < 11 kpc and 1 < ∣z∣ < 2 kpc, separated according to their velocity measurement uncertainties σ(v_ϕ). Stars with small uncertainties, i.e., 0 < σ(v_ϕ) < 1 km s⁻¹ (blue distribution), show a peak at v_ϕ ≈ 250 km s⁻¹, whereas stars with larger uncertainties, i.e., 1.1 < σ(v_ϕ) < 7 km s⁻¹ (red distribution), show a peak at v_ϕ ≈ 200 km s⁻¹.