Relative bias to the inferred value of Φ(400 pc)−Φ(0 pc) using Jeans analysis under the assumption of equilibrium, in the presence of a breathing mode as a function of θ₀. The bias is shown in the bottom panel, where the breathing mode is normalised such that the difference in mean value of w between 400 pc above and below the mid-plane is Δw_400 pc = 1 km s⁻¹ when θ₀ = π/4. The top panels show how the breathing mode phase, θ₀, affects the phase-space distribution. The perturbation is strongly enhanced in the top panels, for better visibility.