Doppler factor as a function of apparent speed for a given viewing angle, δ = f(β_app | θ), and a given intrinsic speed β, δ = f(β_app | β). Loci represent these two functions for a range of θ and β. The values of intrinsic speeds plotted are β = 0.9, 0.95, 0.98, 0.99, 0.995, 0.998, 0.999, 0.9995, and 0.9999 shown as solid lines. For the viewing angle the values are θ = 0.5°, 1°, 1.5°, 2°, 2.5°, 3°, 4°, 5°, 6°, 8°, 10°, 15°, and 30° shown as dashed lines. Note the two different jet regions, in terms of physical characteristics, where components C1 and C3 are travelling. Shaded areas represent the observables from our VLBI monitoring, namely the Doppler factor and the apparent velocity for each of the two knots.