Natural weighted 15 GHz (left panel), 24 GHz (middle panel), and 43 GHz (right panel) VLBA images of PG 1553+113 from the first observing epoch (top image in each panel) to the fourteenth epoch (bottom image in each panel). The vertical separation between images is not proportional to the time difference between epochs. The images at each frequency have been convolved with a common beam with FWHM 0.6 mas × 1.2 mas, 0.4 mas × 0.8 mas and 0.3 mas × 0.7 mas at 15, 24 and 43 GHz, respectively, as shown in the bottom-left corner in each panel. The overlaid lowest total intensity contour is at 0.4%, 1.3%, and 1.8% of the peak at 15, 24, and 43 GHz (see Table 2), respectively, with the following contours a factor of two higher. The colour scale represents the linearly polarised intensity.