Several sources can contribute errors in the measured position of a target.
Inadequate calibrations or calibration parameters which change with time, the position of the target in the field of view, the temperature of the spacecraft prior to and during an observation, spacecraft jitter, the magnitude of the target, unknown duplicity of a target, the color of the target, etc., may all affect the accuracy and precision of a measurement. This precision might decrease for very faint targets and for targets far from the center of the field of view. The precision of the separation measurements is typically 1 milli-arc second.