Power spectra of the the foreground-cleaned CMB maps. Left: TT power spectra evaluated using the UT78 mask. Right: EE power spectra evaluated using the UP78 mask. The thick lines show the spectra of the half-mission half-sum maps containing signal and noise. The thin lines show the spectra of the half-mission half-difference maps, which give an estimate of the noise and some of the residual systematic effects. The black line shows the Planck 2015 best-fit CMB spectrum for comparison.