Error budget for the 70 GHz channel relative to the fiducial B_ℓ. The grey curve represents the error between the full beam and the cutoff approximation used in the window function computations. The colored lines represent the first four modes used in the current beam error model, as described in Sect. 5.3. The black line is the one − σ error obtained by adding the cutoff error and the squared first four eigenmodes.