Comparison of the oxygen abundances estimated through different N₂ calibration relations. Panel a: (O/H) abundances obtained through the N2 calibration relation of Marino et al. (2013) versus the (O/H)_N abundances determined using our expression for the N calibration. The circles indicate the central (intersect) oxygen abundances for our sample of MaNGA galaxies. The plus symbols show abundances (intersect values) at the optical radius R₂₅. The line is that of equal values. Panel b: same as the upper panel but for the (O/H) abundances obtained through the N₂ calibration relation of Pettini & Pagel (2004).