Left: velocity fields derived from disk-models with different geometrical parameters: optical center (cross), PA = 0°, and radial motions of  ~5 km s^-1 (top panel, same as Fig. 2middle-right); shifted dynamical center (circle), PA = 10°, and no radial motions (bottom panel). Contours are the same as in Fig. 2. Right: differences between the observed and the model velocity fields. Contours are at  ±2,  ±4,  ±6,  ±8 km s^-1. The filled circle shows the beam.