At left, difference as a function of the N/O slope of the O/H slopes calculated with a previous N/O calculation and the same slopes calculated assuming a given O/H-N/O relation for all the analysed CALIFA galaxies. The red solid line represents the zero value. At right, comparison between the O/H slopes calculated using this last approach with the same slopes calculated using the O3N2 parameter as calibrated by Marino et al. (2013). The red solid line represents the 1:1 relation. All slopes are expressed in dex/R_e.