Median offset of the strong-line calibrations analysed in this work relative to the high-z sample (z ∼ 1 − 9.5), computed in bins of metallicity. The bins have a width of 0.15 dex and are included only if they contain at least five objects. Each panel corresponds to a different diagnostic. The colour palette is the same as used in Fig. 10 to distinguish between low-z and high-z based calibrations, with markers also representing this division: stars for high-z and squares for z ∼ 0 based calibrations.