Uncertainties on the average distance modulus μ in redshift bins of 0.2: impact of the statistical uncertainty of the training (for SALT2, thin solid curve), calibration uncertainties (dotted curve), residual scatter model (dotted short dashed curve), systematic uncertainty due to SALT2 regularisation (dotted long dashed curve) and differences between results obtained with the two light curve fitters (thick solid curve). Values of α and β that minimise residuals from the Hubble diagram were used.