Residuals for objects in Table 3 having Grade 1 or Grade 2 orbits in the Sixth Orbit Catalog. (a) Observed minus ephemeris residuals in separation as a function of average separation. Points drawn in red indicate systems with ephemeris uncertainties of less than 2 mas. (b) Observed minus ephemeris residuals in position angle as a function of average separation. Points drawn in red indicate systems with ephemeris uncertainties of less than 1°. In both plots, our results in the two filters are averaged for a final result, a dashed line at a difference of zero is drawn to guide the eye, and the curves indicate the ±1σ in estimated uncertainty in our measures as discussed in the text. In both (a) and (b), the gray bar at the left marks the region below the formal diffraction limit.