Comparison of ACT and SPT synchrotron source flux measurements at 150 and 220 GHz. Two types of linear fits are shown: a forced fit with a zero intercept (cyan) and a fit with a free intercept (red). The fits show agreement at the percent level within uncertainties, but there is significant scatter for individual sources. This scatter is likely due to flux variability, as it is similar to the level of scatter seen from year-to-year variations (Sect. 5.1).