Breaks in the radial distributions of oxygen abundances in discs of three galaxies determined via three different calibrations are depicted. The left column panels show the galaxy NGC 0477, where the break radii in the (O/H)_PG16 and the (O/H)_M13,N2 distributions are close to each other and differ from the break radius obtained from the (O/H)_M13,O3N2 distribution. The grey points in panelsa–c are the data for individual spaxels. The line is the broken linear fit O/H – R_g to those data points. Paneld shows the N2 abundance index as a function of the O3N2 index for individual spaxels (grey points) and mean values for bin sizes of 0.2 in O3N2 (dark points). The middle column panels show the galaxy NGC 5320, where the break radii in the (O/H)_PG16 and the (O/H)_M13,O3N2 distributions are close to each other and differ from that in the (O/H)_M13,N2 distribution. The right column panels show the galaxy NGC 5633, where the break radii for the three abundance determination methods are different.