History of ALMA measurements toward PKS 1830−211. (a) Flux-density ratios of PKS 1830−211 NE and SW images (with the color code corresponding to ALMA bands, as indicated at the top of the figure). (b) Flux densities of the NE image of PKS 1830−211, scaled to an equivalent frequency of 300 GHz such as S​_300 GHz = S​_ν × (ν/300 GHz)^α with a spectral index α = −0.7 (error bars indicate a nominal flux uncertainty of 20%) overlaid on top of the Fermi-LAT γ-ray daily-monitoring light curve (in green).