Evolution of the reconstructed annual F_o. The mean curve (black) and 1σ uncertainties (grey shaded area) were computed by 10 000 MC realisations (see text). The green curve represents the smoothed (22-yr SSA) variability. The mean level of 2.5 ⋅ 10¹⁴ Wb defines the grand minima when solar magnetic activity drops below the sunspot formation threshold. Other reconstructions are shown for comparison: that of Wu et al. (2018a, W18) based on the SATIRE-T model applied to ISN (v.2); the same SATIRE-T model but applied to the GSN (W18(GSN)), as well as the OSF reconstructed from space-based measurements (Owens et al. 2017, – O17). Panel B: zoom to the period after 1700. The data are available at the CDS.