Collimation and acceleration of the 1928+738 jet as a function of distance from the black hole. The distance is displayed in units of parsec (top axis) and R_g (bottom axis). Top: intrinsic half-opening angle θ_j as derived from the observed jet width profile. Bottom: Γβ calculated from the proper motions. The shaded area denotes the location where the ACZ terminates, ⟨z_b⟩=(5.6 ± 0.7)×10⁶ R_g.