This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
In beginning to study model drawing the model may be traced upon the slate held between the model and the eye and at right angles to the direction in which the object is seen. (See section 13.) In order to do this with accuracy it is absolutely necessary that the slate shall not move and it is equally necessary that the position of the eye shall not change. As neither of these conditions can be fulfilled exactly without mechanical contrivances for holding both the slate and the bead fixed, it follows that the best tracing one can make will be only approximately correct and even that only if the object is of a very simple character. The more complicated the object the less satisfactory will be the tracing from it. Perhaps the best method is to mark the important angles and changes of direction in the contour with points and then rapidly connect the points with lines following the contours. Although the result may not be very correct, if carefully made the tracing will at least demonstrate the principal points wherein the appearance of an object differs from and contradicts the facts, and that is the sole object of the tracing. It awakens in the student the power of seeing accurately as it teaches the mind to accept the image in the eye as the true appearance of an object even if that image differs from the actual shape and proportion of the object as we know it by the sense of touch. Except as if helps us to learn to see, the tracing gives no training in freehand drawing other than the slight manual exercise involved in drawing the line.