After completing a couple of Bargue plates, the students now are ready to draw from tridimensional objects. The former art academies used this approach to teach the art student how to see the form. With a drawing cast, you have a colorless still standing model which makes it much easier to see the form for a beginning art student. This way the student learns how to see without being distracted by color or little movement like life models do. I´ve been using a sight-size method with this exercise, which basically means that the way you set the subject and the easel allows you to draw the subject in the exactly same size as you see it.