Differential astrometric measurements obtained for J0033−1521, J0045+1634, J0241−0326, and J0355+1133 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 against 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). The NOTCam data are normalized to the OMEGA2000 reference system at the observing epoch indicated by the arrows. OMEGA2000 measurements are plotted as solid circles, while NOTCam and LIRIS data (when available) are shown with open circles and triangles, respectively. The solid curves stand for the best fits to the proper motions and parallaxes. Astrometric error bars are plotted; in some panels, they have the size of the symbols.