Top panel: fiducial primordial power spectrum with a feature around k = 0.125 Mpc^-1 in red and in green contours the 1σ and 2σ dispersion of 100 reconstructions from simulated CMB spectra. The mean of reconstructions is shown in yellow. Bottom panel: residuals ΔC_ℓ between the C_ℓ for the fiducial primordial power spectrum with a feature and the C_ℓ for the best-fit Planck power law in red and for the mean reconstructed primordial power spectrum in yellow. The green bands indicate the 1σ and 2σ bands for the ΔC_ℓ from the simulations, the dashed blue lines show the 1σ region due to cosmic variance.