12 + log(Ne/H) versus 12 + log(O/H) for PNe (dots), and H ii regions (open squares). Same stellar evolution models as in Fig. 6 have been included. In the left panel K10 models, with Z = 0.0001 (blue diamonds) and Z = 0.004 (magenta triangles), and FK14 models, with Z = 0.001 (brown stars), are presented. In the right panel models V1314 (Z = 0.001, red diamonds) and V14 (Z = 0004, green triangles) are shown. The ZAMS initial masses of the progenitor stars are labeled for some models in each metallicity sequence.