1. A digital optical comparator comprising: a holder for holding a part; a light source for illuminating the part; a camera for capturing an image of the illuminated part and a lens placed in front of said camera; and a data processing system for receiving the image, for obtaining a CAD drawing of said part, for displaying said image and said drawing on a computer screen, where said drawing is digitally overlaid on said image, said data processing system further including means for aligning said drawing with said image.