Fit of the two coordinates W(t) and N(t) of component S1 of 1823+568. They correspond to the solution with T_p/T_b ≈ 8.88, M₁/M₂ ≈ 0.17, and i_o ≈ 3.98°. The points are the observed coordinates of component S1 that were corrected by the offsets ΔW ≈  +5 μas and ΔN ≈ 60 μas (the VLBI coordinates and their error bars are taken from Glück 2010). The red lines are the coordinates of the component trajectory calculated using the BBH model.