Brightness temperature spectrum T_B(ν) for the solar disk centre obtained from the data of the INAF radio telescopes (averaged values T_B, av from Medicina, Table 5), and of previous works: Zirin et al. (1991), Subramanian (2004), Ramesh et al. (2006), Mercier & Chambe (2015), Melnik et al. (2018), Kallunki & Tornikoski (2018), Sharma & Oberoi (2020), Zhang et al. (2022). The black continuous line represents the modelled brightness temperature of bremsstrahlung emission obtained by the SSC model (Selhorst et al. 2005, 2019; Zhang et al. 2022); the black dashed line represents the fitted flux accounting for propagation effects; the dark grey shaded area shows the errors in the fit parameters. Green points indicate the measurements obtained from the averaged solar maps of the Grueff Radio Telescope (T_B, av in Table 5), according to the analysis of Pellizzoni et al. (2022) (P+22) and Mulas et al. (2022) (M+22). This figure is an updated version of the figure reported by Zhang et al. (2022).