Example for the calibration results for one test SPD, and for three different G band magnitudes, 13^m, 16^m, and 19^m. Left: difference between the coefficients in the combined basis and true coefficients, normalised to the standard error. The grey shaded regions show the ±1σ_i intervals, the dashed lines the sample mean, and the solid lines the sample standard deviation. Right: coefficients divided by the standard error. The grey shaded regions show the ±1σ_i intervals.