Notes. Column 1: the position angle of the jet symmetry axis in the plane of the sky. Columns 2 and 3: the amplitude and wave scale of the precession. Column 4: the initial phase at the location of MM1. Column 5: the inclination angle of the jet to the plane of the sky.^(†) The inclination i is fixed to 8° according to the calculations using water masers (see Sect. 4). This is because the precession fitting is relatively insensitive to the inclination (e.g. Wu et al. 2009).