Fig. 7. The correlation between the [NII]/H line ratio and the N/O abundance. Dots are the ([NII]6548+6583)/H ratio for each nebula integrated all over the slit length, while the dotted lines give the range of line ratios showed by each object when fluxes are measured locally, i.e. in the spatial resolution elements along the slit. Empty circle represent the data for 32 PNe from KB94.