We used SketchUp because it is simple to use, draws the orthographical views and is free. In this way, it was easy to create the 3D model that is represented in an isometric view (figure 8-a) and the corresponding front, left and top orthographic views (figure 8-b). If the teacher wants it is also possible to add textures to the model to make it look like a real object made of wood for example. This is very easy to do in SkecthUp, by importing a photo texture and add it to the model.