Calibration of the relation ℱ(b_eff) from Eq. (9), required for the conversion of the threshold δ_v, tr in Eq. (7). Left: the 68% and 95% confidence levels in the B_slope–B_offset plane for the void catalogues built both in real (blue) and in redshift space (orange). Right: the solid lines represent the resulting linear relations ℱ(b_eff) obtained with the calibrated coefficients B_slope and B_offset for real (blue) and redshift space (orange), while the shaded regions indicate an uncertainty of 2σ on the relationships. The markers represent the calibration obtained for each bin of redshift, leaving b_punct as the only free parameter of the void size function model when fitting the measured void number counts. This alternative calibration provides a value of b_punct for each redshift of the sample and is associated with the value of the effective bias b_eff of the Flagship galaxies at that specific redshift. As a comparison we also show the linear function calibrated using FoF dark matter haloes in real space by Contarini et al. (2019), displayed with a dashed grey line.