Comparison of the radial distributions of oxygen abundances in the disks of our target galaxies determined through the C method (filled dark [black] circles), via the O3N2 calibration (open gray [red] circles), and through the N2 calibration (plus signs). The solid line in each panel is the best linear fit to the (O/H)_C abundances (the same as in Fig. 8). (A color version of this figure is available in the online version.)