Upper panel: mean SED in MJy² sr⁻¹ for the 100 SIM3 cross-spectra as a function of the effective frequency (, in GHz) for the multipole bin centered at ℓ = 80. The MBB (solid black), first- (dashed yellow), second- (dashed-dotted blue), and third-order (dotted red) best fits are displayed and not distinguishable. Bottom panel: relative percentage difference between the SIM3 SED and the MBB (black diamonds) and the first- (yellow diamonds), second- (blue diamonds) and third-order (red diamonds) best fits.