tokens: and the radio core is typically within 10%. The apparent displacement vectors of C7 have an anisotropic distribution and show asymmetry in the jet direction with tendency to be longer along the jet axis. These effects are most likely due to resolution-dependent core shift or opacity effects. We developed a statistical tool for estimating the mean and variance of the displacements of the core and C7. We find that the displacements of C7 (isotropic component) and the core (anisotropic component) have an almost commensurate contribution to the apparent displacements of C7. The estimates of statistical characteristics of displacements are close to true values for short observation intervals ( 35 days). The rms of displacements of the core and C7 decreases 1.5−2 times during the stable jet state compared to those during the swinging activity of C7. The contribution of the core and C7 to the apparent motion of C7 remains of comparable importance during both states of activity. The rms of the spatial displacements of the core is a factor of four larger than those of the C7. During the jet stability period, the motion of the C7 on time scales of months is complex, showing swinging motion with reversals of the direction, and superluminal speeds. The trajectories of C7, smoothed over time scales of a few years, show a clock-wise loop motion with mean subrelativistic speed (0.16 ± 0.008) c . Long-term monitoring with high cadence (less than or about a month) VLBA observations at 15 GHz is needed to study the dynamics of the C7. Accurate and low positional uncertainties of the C7 are crucial for identifying the dominant contribution of the intrinsic motions of the core and C7 to the apparent motion of C7. We confirm that the excitation of transverse waves moving along the jet is generated by the motion of the C7, which acts as the nozzle to the jet. The excitation of transverse waves with relatively large amplitudes (≳0.2 mas) are associated with excessively large apparent displacement vectors (> 0.08 mas) of the nozzle. Quasi-sinusoidal stable waves with small amplitudes (≲0.02 mas) are generated by the reversal motion of the nozzle within the angular distance of ≈0.02 mas (0.03 pc), which matches nicely with the amplitudes of the excited waves. The on-sky distribution of flux densities of C7 reveals a statistically significant brightening of the emission upstream and transverse to the jet. The observed brightness asymmetry is not dependent on the epoch and it is, rather, associated with a regular change of the jet viewing angle at the location of the C7 (or the nozzle). The asymmetry of the brightness can be reproduced by a toy model of C7. The model assumes an axisymmetric twisted jet velocity field for the C7 and a jet viewing angle of 8°, while the intrinsic flux density and speed of the jet are unchanged. More sophisticated models are necessary to recover the jet viewing angle of the BL Lac and parameters characterising the velocity field of the jet.
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