Metallicity-mass diagram of our sample of quiescent galaxies. The colors indicate different redshift bins, as described in the legend. The gray point indicates the typical error on [M/H]. The stars are the average metallicity values at different mass bins, regardless of the redshift bins, and the associated error bars are the corresponding 16th and 84th percentiles. The solid magenta line is the MEME relation, corresponding to the linear fit containing 99% of the galaxies in each mass bin.