Click the Draw | Tablet | Tablet Calibration command or click the 
button to calibrate the digitizing tablet before beginning work on a project or continuing with a project. The Tablet Calibration Wizard steps through the necessary options to begin a new project or to recalibrate an existing project using the digitizing tablet. The tablet must be calibrated before digitizing objects.
Your paper source documents can be rotated on the tablet, and Didger corrects for any rotation.
Paper source documents can use different scaling in the two dimensions. For example, your document might use a scaling of 1 inch=1000 feet in the X dimension, and 1 inch = 1200 feet in the Y dimension, and Didger corrects for the different scaling.
See Also
Introduction to Tablet Calibration