Comparison of the modeled T_e as a function of T_e measured by CHAOS using the [N ii] λ5755 auroral line. Each panel makes a different assumption about how the value of f_ion and 12+log(O/H) are calculated. The top-left plot represents the best-case scenario, where we vary f_ion as a function of [S iii]/[S ii] and use metallicities calculated from the direct method. This shows the lowest systematic scatter between T_e values of 662 K. The other two plots in the top row each relax one of the assumptions, assuming either a fixed f_ion = 0.97 (top center) or a metallicity calculated from strong line techniques (top right). Both have an increased scatter of ~900 K. The two plots in the bottom row further relax the assumptions, resulting in further inaccuracies. This test includes the assumptions of both a fixed f_ion = 0.97 and a strong-line metallicity (~950 K; bottom right) and a fixed f_ion = 0.97 and a fixed global metallicity per galaxy (~1100 K; bottom center). A one-to-one relation (solid line) and 1σ scatter (dotted lines) are shown in each plot, and the median and standard deviation are listed. While relaxing our assumptions does result in increased scatter, the overall agreement remains good. We adopt the assumptions that go into the top-right figure (a variable f_on and a strong line 12+log(O/H)) for the model that we apply in this work, as summarized in Sect. 4.3.