Similar to Fig. 6, however, for the target source FU Ori and is presenting the measurements at 271−274 GHz. Horizontal axes of the top and middle panels are presented on the same scale. There were only two epochs of 225 GHz observationson FU Ori. However, one of them (November 09, 2013) was taken at an extremely poor weather condition (τ_225 GHz ~ 0.4), such that the absolute flux calibration was very uncertain. Middle and bottom panels present the gain calibrators for the 271−274 GHz observations(0530+135) and the 225 GHz observations (0510+180), respectively.