Power spectra of 70, 100, and 143 GHz maps evaluated after masking approximately 40% of the sky. Top: cross-spectra of half-ring maps at 70 GHz and half-mission maps at 100 and 143 GHz, as well as the spectra of the half-difference maps, which illustrate the noise content of the data. Binned 143 GHz raw cross-spectrum values indicate the bin centres; the other spectral values are spread in the bins for clarity (see further details in text). Bottom: power ratios of the same spectra. The drop in the values of some ratios at ℓ <  150 is due to uncorrected diffuse foreground emission that gets brighter at 143 GHz outside the masked part of the Galaxy. At ℓ >  150 there is excellent consistency of all three spectra. One can see that at the top of the first acoustic peak near ℓ ≃ 220 they are consistent at the level of a few ×10⁻³.