But above all, the best thing is to draw men and women from the nude and thus fix in the memory by constant exercise the muscles of the torso, back, legs, arms, and knees, with the bones underneath. Then one may be sure that through much study attitudes in any position can be drawn by help of the imagination without one’s having the living forms in view.
Giorgio Vasari, Vasari on Technique, trans. L. S. Maclehose, Dover Publ., 1999, p. 210
I'd like to offer two alternative points of view on the dominant method of instruction in modern “classical” ateliers, sight-size. One has to do with its deleterious effects on the artist’s capacity for memory and invention. By relying on a mechanical measuring technique rather than developing an intuitive sense of judgment—of scale, proportion, shape—the artist is incapable of inventing the figure, which is traditionally what all classical artists aspired to do. If sight-size is perhaps most effective as a portraiture technique, portraits are actually a small part of what constitutes the classical tradition in painting. What was once known as history painting—narrative and allegorical works—depended on a command of inventing the figure in a variety of poses and positions. These were often studied in detail with reference to a model, but more as a corrective to the artist’s imperfect memory than a documentation of a figure in costume according to a specific pose. Science is telling us that memory and imagination are naturally conflated in our brains, and the classical tradition depended on that richly contaminated interplay between memory and imagination. Drawing from the model was meant to train the memory, not generate a photographic likeness of the subject.
The other issue, maybe more insidious, is the historical inaccuracy of claiming that sight-size is part of a long-standing Old Master tradition. It is not. It may, in fact, be an invention of the late nineteenth or early twentieth century. The fictive pedigree of the sight-size method is not only injurious to the historical record, it deludes artists who believe they are working like the Old Masters, when they decidedly are not. As one form of proof, images of artists at work in the classical tradition are illuminating. If sight-size involves positioning the artist’s work in a fixed, orthogonal position to the subject and working at precisely the same size as the subject appears (with plumb line and measuring tools), no artist before the twentieth century shows artists at work in that way. In the classical (not realist) tradition, artists at work were often shown allegorically (Allegories of Painting), or as historical artists at work: St. Luke painting the Virgin and Child, or Apelles painting Campaspe. What follows is a catalogue of those images, working backwards chronologically from the eighteenth century to the sixteenth. What’s obvious is that the artist is not working one to one en parallèle to their subject. They are often turning, peering around the canvas, looking up, and/or working at a different scale. The fictive canvas is almost always oblique to the subject and to the painting itself. By continually looking from the subject to the canvas the artist is relying in one way or another on their short-term memory to translate what they had seen onto the canvas.
 Hans-Peter Szameit at The Swedish Academy of Realist Art has this thoughtful assessment and critique of the sight-size method: