Difference between metallicity estimates (12 + log₁₀(O/H) defined in Eq. (1)): a comparison of the metallicities measured for some of our galaxies in the literature (Nakajima et al. 2022, 2023; Sanders et al. 2024) via auroral lines, with our own estimates. At relatively high metallicities, above 12 + log10(O/H) ∼ 7.4–7.6 (that is Z/Z_gas 0.1–11% Z_⊙), the differences remain within σ(12 + log₁₀(OH))<0.05. This is about the same dispersion between other metallicity estimates, although on a smaller sample. However, there is a disagreement at lower metallicities, and CIGALE's 12 + log₁₀(O/H) present an offset that might be systematic or increasing with lower metallicities by about σ (log₁₀(O/H)) < 0.10. But the direct method is not well calibrated at log₁₀(O/H) < 7.4–7.6 because there are less than 5 objects with auroral lines at such low metallicities estimated via the direct-method oxygen abundances.