Offset between the observed metallicity in the different samples of z ∼ 0.9 and z ∼ 2.3 galaxies and the predicted metallicity based on their M_* and SFR, according to the FMR defined by SDSS galaxies at z ∼ 0 by Eq. (1) in M10 and Mannucci et al. (2011). All the data points are based on single measurements on stacked spectra in mass and SFR bins; the error bars show the corresponding metallicity uncertainty, except for Steidel et al. (2014), whose medians of single galaxies in mass bins are plotted with their dispersion as a dashed line. The grey area shows the ±0.1 dex region around 0, which represents an estimate of the uncertainty tied to the FMR extrapolation and parameter estimation in the range covered by the data points (see Curti et al., in prep.). Once the FMR and the measured metallicities are plotted on a consistent scale (in this case Maiolino et al. 2008 calibration), no apparent evolution of the FMR up to z ∼ 2.3 is found.