 an image of the eyeglasses; a processor and associated display configured to perform at least the following: calculating an editable outline for each eyepiece of the eyeglasses and display said outline and said image, such that the editable outline can be compared to a respective eyepiece of the image; calculating supplemental locations associated with the outline for anchoring parts of an add-on unit; and providing data indicative of at least said outline and said supplemental locations