Estimation of the [Mg/Fe] dispersion of the metal-poor bulge sequence in the [Mg/Fe] versus [Fe/H] plane. Upper panel: black points stand for the whole close-to-the-plane bulge sample. The stars of the Mg-rich sequence with [Fe/H] >  −1.0 dex are highlighted in red, with error bars accounting for their individual abundance measurement errors. A running median for these stars is displayed as a blue solid line. A fourth-degree polynomial model fit on the data is displayed by the black dashed line. Lower panel: residuals distribution from the polynomial fit. The dashed black line depicts the zero bias level. The standard deviation of the residuals is quoted in the panel.