Quantities used in determining the value of φ_sky (Eq. (8)) for radiometer LFI-27M (30 GHz) during a short time span (2 min). Panel A): the quantities B_mb ∗ T_CMB and B_sl ∗ T_CMB are compared. Fluctuations in the latter term are much smaller than those in the former. Panel B): the quantity B_sl ∗ T_CMB shown in the previous panel is replotted here to highlight the features in its tiny fluctuations. That the pattern of fluctuations repeats twice depends on the scanning strategy of Planck, which observes the sky along the same circle many times with a spin rate of 1/60 Hz. Panel C): value of φ_sky calculated using Eq. (8). There are several values that diverge to infinity, which is due to the denominator in the equation going to zero. Panel D): distribution of the values of φ_sky plotted in panel C). The majority of the values fall around the number + 0.02%.