Observed auroral-to-strong line ratios and CLOUDY-generated auroral-to-strong line ratios plotted as functions of binning metallicities for [O II] (upper left), [S II] (upper right), [O III] (lower left), and [S III] (lower right). Lines in the panels represent the data generated by CLOUDY and are color-coded by ionization parameters (the left color bar). Dots in the panels represent the observed data and are also colored by ionization parameters (the right color bar). In the lower left corner of each panel, the black error bar shows the median uncertainty of the observed data. Observed data have a significant offset from the models.