Mean [O iii] electron temperatures, computed according to Eq. (1), for all α = 3 nebular models as function of the post-AGB age (left) and stellar effective temperature (right). In the right panel, the models are only plotted until maximum central star temperature (corresponding to a post-AGB age of  ≃9800 years in the left panel) in order to avoid confusion due to overlapping lines. The grey area depicts approximately the region occupied by the hydrodynamic models presented in Paper I and Paper IV which have all Z = Z_GD, but various initial conditions and central stars.