Error on the mean redshift determination, ⟨z⟩−⟨z⟩_truth, in ten Euclid tomographic redshift bins, for each of the four galaxy bias correction strategies (Sect. 3.1), compared via the shifted-true model (Sect. 3.3.1). In dark blue is method 1, where no corrections are applied; in purple is method 2, where the spectroscopic galaxy bias is calibrated by spectroscopic auto-correlations; in magenta is method 3, where the photometric galaxy bias is calibrated by a power-law fit to noisy, photo-z-binned photometric auto-correlations; and in light pink is method 4, where the photometric galaxy bias is calibrated using auto-correlations binned by true redshifts (not applicable to real data). Dark and light shades indicate 68.3% and 95.5% confidence intervals. The grey band shows the target uncertainties for Euclid. Method 4 shows that systematic biases in bins 1–6 are caused by incomplete bias corrections, whilst the biases persist for higher-redshift bins, suggesting some other source of systematic error.