For each of the HFI channels, the difference of the normal spectrum and the spectrum obtained with a more severe selection of rings, is shown in units of the expected standard deviation. If our assumptions are correct, the residual noise is supposed to have a Gaussian distribution centred on zero with a dispersion of one. The red points for the 143 GHz correspond to a sanity check with a random discarding of rings as discussed in Fig. B.3 (the points here are band-averaged in bins of width Δℓ ~ 31).