Left: (u, v) coverage for 3C 279 observations in band 3 on 2018 April 21 (colored points), showing the overlap between ALMA–LMT and ALMA–SPT baselines (highlighted with a box). Right: band 3 flux densities on ALMA–LMT (blue) and ALMA–SPT (orange) as a function of the projected baseline length in the east-west direction, in units of wavelength, demonstrating the under-calibration of amplitudes on LMT baselines. HOPS data are shown in this figure, but are consistent with that from CASA.