Same as Figure 4, but here we include six panels arranged in three rows by two columns, each showing the relation between directly measured N/O and the observed emission-line ratios [N II]/[O II] (left column) and [N II]/[S II] (right column). Each row adopts a different colour coding: redshift (top), gas-phase metallicity derived via the direct method (middle), and [O III] electron temperature, T₃ (bottom).