Comparison of low-ℓ half-mission polarization EE (left) and BB (right) power spectra. Each spectrum is computed as the difference between the respective half-sum and the half-difference spectrum. Grey bands show 1σ confidence regions derived from 300 end-to-end simulations as processed by Commander. Formally speaking, these can therefore only be directly compared with the red curve. Note that the value for the optical depth of reionization adopted for these simulations is τ = 0.060 (see Planck Collaboration II 2020; Planck Collaboration III 2020 for details), which is larger than the best-fit Planck 2018 value of τ = 0.054.