Stellar mass-stellar metallicity plane. Blue line and band: SDSS stellar mass-metallicity relation from Gallazzi et al. (2005). Gray dotted line: dwarf–galaxy relation from Kirby et al. (2013), converted to total metallicity and stellar mass as discussed in the text. Colored symbols: NGC 1427A measurements in three apertures (gold = whole galaxy; green = main body; purple = northern clump). Filled circles show pPXF mass-weighted metallicities ⟨[Z/H]⟩_MW; open circles show light-weighted values ⟨[Z/H]⟩_LW, with vertical connectors.