a) Bias ⟨ δS_k(Ξ_I) ⟩ _k (in blue) drift continuously with time. It equally affects all 72 residuals of the fit S(Ψ) vs. Ψ. When corrected, the width of the residual distribution is reduced to its photon statistics value (Fig. 20a). This correction is equivalent to a modification of the flux scale Ψ_I→Φ_I. b) The flux ramp sequence Ψ_I (red), taken from Fig. 16, is correlated to the dispersion of biases (error bars in Fig. 19-a). For Ψ_I < 2000 adu (black boxes) the dispersion of the pedestals dominates the dispersion of the photon number.