Also from the article:
>The difference between traditional approach and sight-size method is very important. In order to draw, the student needs to develop the ability to measure proportions visually: every part must have the same relationship to other parts in size as it is on the model. For example, the vase is so much bigger than the cup, or the head is so much smaller than the ribcage, etc. The ability to see each part in relationship to the whole and therefore keep all of the parts in the same scale, is not easy to attain and takes years of constant practice. After years of practice, one can draw or paint in any scale they like. This is the essential aspect of drawing, and is the biggest reason why academies had exams and would not accept students who did not develop this ability. Some professors at the nineteenth century Russian academy demonstrated the level of virtuosity by drawing, for example, the statue of Laocoon starting from the small toe all the way to the head in perfect proportions; or drawing parts of the model on separate pieces of paper, mentally keeping them in the same scale, and then, when they put them together, all of the parts fit together perfectly to the astonishment of the students.
>The sight-size tracing method bypasses the need for proportional measurement and directly traces the points from the model to the surface, evading a serious and lengthy study of proportion and form. If the student does not quit this practice fast enough, he or she will end up lacking proportional measurement skills and with a severe dependency on this mechanical method.