Evolution of corrections factors. Top left panel: the theoretically predicted variations of V_post/V_[N ii] with absolute stellar magnitude, M_V, are compared with observationally determined values of V_post and V_[N ii] for PNe for which both velocities are known (see Table A.1). The maximum value of V_post/V_[N ii] is 7.1 right after the thick/thin transition of the 0.595 M_⊙ “α = 3” model sequence. Bottom panel: here the ratio vs. absolute stellar magnitude is plotted for the same simulations shown in the top left panel. Top right: observed line profile of [N ii] λ 6583 Å (circles) of the PN NGC 6629 (No. 196), taken from Paper II compared to a theoretical profile computed from a model of the 0.595 M_⊙ “α = 3” sequence, convolved with a Gaussian of 10 km s^-1 FWHM. This model corresponds closely to the position of NGC 6629 in the top left panel, and its parameters are the following: T_eff = 46 800 K, (post-AGB) age = 3968 yr, and M_V = −0.58, V_[N ii] = 5.6 km s^-1, and V_post = 34.4 km s^-1. Observed values are T_eff = 47 000 K (Méndez et al. 1988), M_V = −0.41, V_[N ii] = 6 km s^-1, and V_post = 34 km s^-1 (see Table A.1, No. 196). The vertical dotted line indicates the shock velocity of the model, Ṙ_out = 41 km s^-1.