This paper investigates the impact of metallicity calibrations, AGN classification, and aperture covering fraction on the local mass-metallicity relation (MZ relation) using 27,730 star-forming galaxies from the Sloan Digital Sky Survey (SDSS) Data Release 4. The authors analyze the MZ relation with 10 different metallicity calibrations, including theoretical and empirical methods. They find that the choice of metallicity calibration significantly affects the shape and y-intercept of the MZ relation, with absolute metallicity scale variations up to Δ[log(O/H)] = 0.7 dex. To address this issue, they present new metallicity conversions that allow metallicities derived from different strong-line calibrations to be converted to a common base calibration, reducing discrepancies to within 0.03 dex on average. The study also examines the effect of AGN classification and aperture covering fraction on the MZ relation, finding that different AGN classification methods have negligible effects, while aperture effects are significant for galaxies with high stellar masses and low redshifts. The results highlight the importance of using consistent metallicity calibrations when comparing different luminosity-metallicity or mass-metallicity relations.This paper investigates the impact of metallicity calibrations, AGN classification, and aperture covering fraction on the local mass-metallicity relation (MZ relation) using 27,730 star-forming galaxies from the Sloan Digital Sky Survey (SDSS) Data Release 4. The authors analyze the MZ relation with 10 different metallicity calibrations, including theoretical and empirical methods. They find that the choice of metallicity calibration significantly affects the shape and y-intercept of the MZ relation, with absolute metallicity scale variations up to Δ[log(O/H)] = 0.7 dex. To address this issue, they present new metallicity conversions that allow metallicities derived from different strong-line calibrations to be converted to a common base calibration, reducing discrepancies to within 0.03 dex on average. The study also examines the effect of AGN classification and aperture covering fraction on the MZ relation, finding that different AGN classification methods have negligible effects, while aperture effects are significant for galaxies with high stellar masses and low redshifts. The results highlight the importance of using consistent metallicity calibrations when comparing different luminosity-metallicity or mass-metallicity relations.