tokens: role of the hydrodynamic effects, we compare a 3D hydrodynamic simulation, published in Nawaz et al. ( 2016 ), to a ballistic jet model (Gower et al. 1982 ) for the precessing jet source Hydra A in Fig. A1 . Model parameters are given in Table A1 . It is clear that even for this comparatively low-power jet, the curvature induced by precession dominates the observational appearance for most of the region where the jet is observed. It is therefore reasonable to take curvature as signature for precessing jets. Figure A1. Different methods of modelling the precessing jet in Hydra A. (a) VLA image of Hydra A. (b) Hydrodynamic simulation of a jet with parameters empirically matched to Hydra A. (c) Ballistic jet model (Gower et al. 1982 ) for Hydra A. Even though Hydra A has a weaker jet than the powerful jet sources discussed elsewhere in this article, the jet path is over most of its length well modelled by the hydrodynamic simulation as well as the ballistic model. This suggests that precession effects are indeed observable in real radio sources. Panels (a) and (b) were adopted from Nawaz et al. ( 2016 ). Table A1. Parameters for the jet models compared in Fig. A1 . a Ω t ref in Gower et al. ( 1982 ). APPENDIX B: RADIO MAPS FOR THE COMPLETE SAMPLE We provide here all the radio maps of our complete sample. Shown is Stokes I in Jy beam −1 . The mapping of the flux levels onto the colour map is non-linear and has been adjusted carefully for each map to ensure lobe and jet structures are well visible. Equatorial coordinates are given on the maps. Observing frequency, resolution, redshift, and precession indicators are given in the individual figure captions. The features of precessing jets are indicated on each map if applicable. Figure B1. 3C 20, 8.41 GHz, resolution: 11, redshift: 0.174. C: Curved jet structure on the eastern side. E: Lobe brightness asymmetry/jet at edge of lobe on the western side. R: Multiple terminal hotspots on the eastern side; wide terminal hotspot on the western side. S: S-symmetry. Additionally, interaction with ambient medium. Figure B2. 3C 22, 8.56 GHz, resolution: 075, redshift: 0.938. C: Curved jet. E: Misaligned lobe axis on the eastern side. Lobe brightness asymmetry on the western side. S: S symmetric jets. Figure B3. 3C 33.1, 4.85 GHz, resolution: 2948 × 2472, redshift: 0.18. C: Curved eastern jet. E: Misaligned lobe axis on the eastern side. S: S-symmetric jets. Jet enters lobe on southern side. Jet bends with brightening, possibly related to jet–cloud interaction. Southern tip-of-lobe hotspot lies along the continuation of inner southern jet. The innermost part of the jets is aligned with the lobe axis [solid black line, position angle (jet side) indicated]. Figure B4. 3C 41, 8.46 GHz, resolution: 02, redshift: 0.795. C: Curved southern jet. E: Misaligned lobe. R: Wide terminal hotspots on both sides. S: S-symmetric jet–hotspots. Southern jet (yellow dotted line) misaligned with lobe axis (solid white line) by
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