RP simulations, using the synthetic spectral energy distribution library of Lejeune et al. (1997), of the effect of ±10% dispersion variation (left), LSF conditions in the seven CCDs (centre), and both effects together as expected in each CCD (right), for a star with an effective temperature of T_eff = 3350 K. The ±10% dispersion variation considered in the left plot represents the maximum variation expected for the different observations. The dispersion at a given time of the mission changes across the focal plane with the CCD. The latter effect is included in the plot at the right.