Some relations for the inner precessing nozzle model. Top panel: modeled relation between the ejection position angle and the initial viewing angle, denoting the PA range of ~ 20° (from 20° to 40°) and the viewing angle range of ~ 0.54° (from 1.23° to 1.77°). The precession axis is at (30.14°, 1.50°). Middle panel: Modeled PA(t) and the modeled position angles of knots C1–C6. Lower panel: flux density variations of the VLBI-core and the total source at 15 GHz and the Doppler beaming ratio (assuming Lorentz factor Γ = 10 and α_r = 0, it has a maximum of 1.15) are shown, indicating that the flux variabilities are not correlated with the periodic Doppler beaming produced by the jet precession and the intrinsic nonregular variations dominates. The tick marks denote the ejection epochs of the knots C1–C6.