Comparison between fits to the derived O/H radial distributions at a galactocentric radius less than 3R_e (horizontal axes) and less than 5R_e (vertical axes). Upper panel: comparison of the extrapolated O/H abundances in the galaxy centres. Lower panel: comparison of the slopes of the fits. The oxygen abundances and their corresponding gradients were derived using the following two methods: the R calibration (black circles) or the HCM code (green triangles). Dashed lines represent the one-to-one correspondence.