Relation between N/O ratio measured using the T_e method and the N2O2 (upper panel) and N2S2 (lower panel) diagnostics for our full high-z auroral-line sample. For comparison, we include local galaxies with auroral-line detections from the literature as grey points (see references in Sect. 2.1.3). The local calibration from Pérez-Montero & Contini (2009) is shown in blue and a fit to the SDSS stacks of Curti et al. (2017) is given in green. In both panels, the grey error bar in the top left corner represents the median measurement uncertainty of the local comparison sample. The solid red line shows the best fit obtained from the high-z sample, with the uncertainty range shaded.