Histogram of heights from the Galactic plane, as measured from the Sun (Z = z − z₀), for a) OCs and b) ECs, using a bin width of ΔZ = 10 pc and Poisson uncertainties. The overplotted solid curve in each panel represents: a) the fitted Z-distribution Φ_Z(Z) from Eq. (10) with best-fit parameters z₀ = 14.7 ± 3.7 pc and z_h = 42.5 ± 9.9 pc; b) the predicted Z-distribution from Eq. (10), using the parameters fitted for the OC sample. In panel b), the darker shaded region is the Z-histogram for ECs with distances D < 4 kpc, whereas the dashed curve indicates the corresponding distribution as predicted from Eq. (10) and the same parameters z₀ and z_h.