Diagram of jet precession. The precession angle ψ is the angle between the jet axis and the precession axis, and the diagram uses a fiducial value of ψ = 30°. The polar viewing angle, θ, is the angle between the precession axis and the viewing angle, with the angles used in Figure 3 shown. Not shown are the azimuthal viewing angles, which are rotated around the precession axis in increments of Δϕ = 45°. A cyan arrow indicates the direction that the jet axis precesses.