Bias in the CMB B-mode power spectrum reconstruction for SO-SAT dataset. The ratio between the bias (see Eq. A.3) and the input CMB power spectrum . All angular power spectra are computed as the average among 200 different simulated NILC CMB reconstructions and adopting the masks employed in Sect. 5. The shaded regions display the relative uncertainty computed as . Left: Results of the application of r-NILC. Right: Bias from the ZB (blue) and hybrid ZB-NILC (red) methods. In all cases input foregrounds emission was simulated assuming the d1s1 sky model.