Best-fit spectra of BL Lac observed with BeppoSAX during the soft state in 1999 transition (dataset “S3”) in E ∗ F(E) units for the model fits (from left to right): phabs*bbody (green line, for 79 d.o.f.), phabs*powerlaw (purple line, for 79 d.o.f.), phabs*(bbody+powerlaw) (light-blue line, for 77 d.o.f.) and phabs*BMC (red line, for 77 d.o.f.). The data are shown by black crosses. For an additive model, phabs*(bbody+powerlaw), the model components are presented by dashed blue and red lines for blackbody and powerlaw, respectively (see details in Table 6).