For a correct design we must create blocks with the following properties:

• Its coordinate origin must be in the same place as in the primitive (or object) in SL.
• It must have associated three attributes called PRIMROTATIONX, PRIMROTATIONY y PRIMROTATIONZ.

To generate a block with this characteristics we must follow these steps

To define a cube of  1x1x1 m and convert it in block en with the coordinate origin in the center of gravity we'll do the following:

• In the Drawing menu, choose Solid and rectangular Prism.

• Reading in the command line, we will define the base point, pressing into de drawing space or typing the coordinates. One good option it will be 0,0,0

• We will choose Cube, and, as length, 1. 

• To change from the Top view to a Perspective view we use View->3D View->Isometric SO.

• To improve the visibility, using 3D Orbit, we rotate the drawing draging from one of the horizontal symbols.

• Next we'll draw some lines wich serve as basis to locate the COG (Center of gravity) of the solid. We'll use the comand “Line”, toolbar Draw, or from the menu Drawing->Line.
• Activating End Point and Midle point reference it will be much more easier. We'll look at the bottom button called REFENT, right click ->options, and then we will check End Point and Midle point .