Naturally weighted total intensity CLEAN image of 3C 273 at 15.4 GHz (top). The alignment error (in beam widths) along the jet as a function of frequency ratio (middle). The alignment error (in beam widths) perpendicular to the jet (bottom). The error is defined as r_ν1−r_ν2 where r_ν1 is the position in the low-frequency image and r_ν2 is the corresponding position in the high-frequency image. The different spectral index gradients are shown in different colors: −0.1 mas^-1 (black squares), −0.2 mas^-1 (blue crosses), and −0.3 mas^-1 (red circles).