Before you begin calibrating, you must select at least three calibration points either on the Image Source in the Image Registration and Warping dialog for an image or the Tablet X and Tablet Y in the Create Calibration Points dialog for a tablet. Calibration points can be bench marks, surveyed points, grid intersection lines, axis intersections, or any type of identifiable point you choose. These points are entered into the calibration points table.
Calibration points can be at any location and are important in establishing the quality of your subsequently digitized data. The accuracy also depends on the degree of precision you use when digitizing the calibration points.
The calibration points cannot lie in a straight line. If you can, spread the calibration points over the extent of the document or image.
Calibrating Large Documents
Tablet Calibration Wizard
Creating Calibration Points