The upper panel presents the observed spectra of COCONUTS-1B (black) with 1σ measurement uncertainties (gray shadow) and the Sonora atmospheric model spectra interpolated at the parameters drawn from the MCMC chains (purple). The lower panel shows the fitting residual (data–model; black), and the purple shadows are the 1σ and 2σ dispersions of 50,000 random draws from the covariance matrix, composed of measurement uncertainties along the diagonal axis.