Differential astrometric measurements obtained for J0501−0010, J1022+5825, J1726+1538, and J2208+2921 in the time interval from 2010 January through 2012 December. For each object, the top and middle panels depict the apparent trajectories of dα and dδ, respectively, and the bottom panel illustrates dδ as a function of dα, where north is up and east is to the left. The reference epoch (2010 January) of the OMEGA2000 data corresponds to (dα, dδ) = (0, 0). Symbols as in Fig. 3.