Effect of changing the zero-point in the g MegaCam filter by 10 mmag on light-curve parameters and distance modulus as a function of redshift for SNe in the low-z (blue crosses), SDSS (green squares), SNLS (orange circles) and HST (red ×) samples. The effect on the distance modulus is computed using the fiducial values α = 0.14 and β = 3.15. The dots show the numerical values of the derivatives (including numerical noise) before smoothing.