Metallicity distributions of stars in Eridanus 2. From left to right: metallicities as predicted by full-spectrum fitting with a synthetic stellar-template library, predicted metallicities based on our observations for stars with a signal-to-noise ratio S/N >  10 determined with a transfer-learning algorithm, and metallicities by Li et al. (2017) for a different sample of stars. The black vertical dashed lines indicate the range of metallicities we have used for isochrone calculation, based on the distribution determined by Li et al. (2017).