Planck 70, 100, and 143 GHz CMB anisotropy power spectra computed for the GAL060 mask. Mask- and beam-deconvolved cross-spectra of the half-ring maps show the signal; auto-correlation spectra of the half-ring difference maps show the noise. Points show single multipoles up to ℓ = 1200 for 70 GHz and ℓ = 1700 for 100 and 143 GHz. Heavy solid lines show Δℓ = 20 boxcar averages. The S/N near the first peak (ℓ = 220) is approximately 80, 1900, and 6000 for 70, 100, and 143 GHz, respectively. Noise power is calculated according to the large-ℓ approximation, i.e., as a distribution with mean C_ℓ and rms C_ℓ [ f_sky(2ℓ + 1)/2 ] ^{− 1/2}. Pairs of thin lines mark ± 3σ bands of noise power around the noise spectra. We translate this statistical spread of noise power C_ℓs into the signal spectra estimated via half-ring map cross-spectra. Under the simplifying assumption that each C_ℓ of the noise in the cross-spectrum at high-ℓ is distributed as a sum of (2ℓ + 1) products of independent Gaussian deviates, each with variance derived from the half-ring difference maps, the Gaussianized high-ℓ noise in the cross-spectra has zero mean and rms of . Pairs of thin lines mark ± 1σ bands of noise around the boxcar-averaged cross-spectra.