Planck 2013 results. XXXI. Consistency of the Planck data
  The Planck design and scanning strategy provide many levels of redundancy
that can be exploited to provide tests of internal consistency. One of the most
important is the comparison of the 70GHz and 100GHz channels. Based on
different instrument technologies, with feeds located differently in the focal
plane, analysed independently by different teams using different software, and
near the minimum of diffuse foreground emission, these channels are in effect
two different experiments. The 143GHz channel has the lowest noise level on
Planck, and is near the minimum of unresolved foreground emission. In this
paper, we analyse the level of consistency achieved in the 2013 Planck data. We
concentrate on comparisons between the 70/100/143GHz channel maps and power
spectra, particularly over the angular scales of the first and second acoustic
peaks, on maps masked for diffuse Galactic emission and for strong unresolved
sources. Difference maps covering angular scales from 8deg-15arcmin are
consistent with noise, and show no evidence of cosmic microwave background
structure. Including small but important corrections for unresolved-source
residuals, we demonstrate agreement between 70 and 100GHz power spectra
averaged over 70<l<390 at the 0.8% level, and agreement between 143 and 100GHz
power spectra of 0.4% over the same l range. These values are within and
consistent with the overall uncertainties in calibration given in the Planck
2013 results. We also present results based on the 2013 likelihood analysis
showing consistency at the 0.35% between the 100/143/217GHz power spectra. We
analyse calibration procedures and beams to determine what fraction of these
differences can be accounted for by known approximations or systematic errors
that could be controlled even better in the future, reducing uncertainties
still further. Several possible small improvements are described...(abridged)
