Average vector residuals in milliarcseconds (scale at lower left) as a function of position within Channel 37 from the full Schmidt 14 parameter modeling of Channel 21 and Channel 37 described in Section 4.3. All positions have been re-origined to the CCD center. Note the extreme variation in vector length and position angle over small spatial scales, for example, the grouping consisting of stars 22 through 34 (row ~ 50, column ~−200). Comparing Channel 21 with Channel 37 demonstrates serious astrometric systematics on very small spatial scales.