The locations of knots B and C in 1983 are denoted by triangles, and we include an estimated 15 mas error on the position based on a typical centroiding error of 10% of the beam size (0.15″). Optical data are identical to that described in Fig. 2. For knot C, a dashed line gives the fit to epochs 1983 and 1994. For knot B, the dashed line is a parabolic fit to all data. The location of knot A is noted with a dotted line.