Abstract: A method and apparatus for calibrating the scan of a laser over a planar surface that includes defining an error table having x-dimension and y-dimension correction factors, and also a scale factor, for each of a plurality of regions of the planar target surface. The scale factor is initially set to a value to account for differences in the size of the image field to be scanned and the overall scan field in the CAD data base. Adjustment is performed to each scale factor to account for theoretical differences due to the use of a perpendicular galvanometer-driven mirror scanning system. A sheet with a large number of square cells is then placed over the target surface, after rotational alignment, and the laser marks each cell. The sheet is then converted into digital form by scanning, and the location of the laser mark relative to the centroid of the cell is used to update the correction factors for that cell.