T−T summary plot of four different simulations. Each coloured line corresponds to the best-fit to a single HEALPix N_side = 8 region, evaluated from underlying an N_side = 256 synchrotron-only simulation. The top left panel shows the ideal case with neither spurious offsets nor instrumental noise; all lines converge perfectly on the origin. In the top right panel spurious offsets of −30 and +20μK are added to the two frequencies, resulting in a simple corresponding translation of the entire plot. The bottom left panel shows the effect of a spurious dipole; the lines no longer converge on a single point, as each region is effectively translated by a different offset. Finally, the bottom right panel illustrates the effect of instrumental noise.