Comparison of weighted and unweighted mean azimuthal velocities 〈v_ϕ〉 as a function of Galactocentric radius for four vertical slices in ∣z∣. Stars with small errors (σ(v_ϕ) ∼ 1–2 km s⁻¹) tend to rotate faster (v_ϕ ∼ 250 km s⁻¹), while stars with larger errors (σ(v_ϕ) ∼ 5–7 km s⁻¹) typically rotate more slowly (v_ϕ ∼ 220 km s⁻¹). Weighting by 1/σ² therefore shifts the mean toward the kinematics of the low-error subpopulation, introducing a systematic offset.