The design team(s) responsible for the exterior of the vehicle develops the proportions, shape, and surface details of the vehicle. Exterior design is first done by a series of manual sketches and digital drawings. Progressively, drawings that are more detailed are executed and approved by appropriate layers of management, followed by digital rendering to images. Consumer feedback is generally sought at this point to help iteratively refine vehicle concepts according to the targeted market and will continue throughout the rest of the design refinement process. After more progressive refinement, industrial plasticine and or digital models are developed from and along with the drawings and images. The data from these models are then used to create quarter-scale and finally full-sized mock-ups of the final design. With three- and five-axis CNC milling machines, the clay model is first designed in a computer program and then "carved" using the machine and large amounts of clay.