Bias in the photometric redshifts due to passband variations as a function of redshift in the MegaCam ugriz + Euclid Y_EJ_EH_E configuration. Each plot shows the bias for the four CWW templates, as indicated. Left: only the r passband is variable; centre: all passbands are variable; right: all passbands are variable, and four exposures have been stacked. In the left plot, the vertical dashed lines indicate the redshifts where the Balmer break enters and exits the r passband. The different curves show the bias when the passband variations are ignored (black line), or when the full central passbands corrected for the shifts in mean wavelengths (blue line) are used. The dashed red lines show the bias when the second-order polynomial correction on the flux presented in Sect. 5.2 is used. We point out that the blue and red lines are very close, so that the blue line is often barely visible.