The MainSurface GCD represents a portion of the part that remains parallel to the press table all through the stamping process. Multiple candidates for the main surface are extracted from the part geometry. Final selection of the main surface is carried out by the cost engine. Very roughly, the cost engine selects the largest flat surface on the part. For highly deformed parts, the cost engine looks for the largest surface, ignoring its flatness. For parts with many bends, the cost engine selects a flat surface that minimizes the number of bend stages or stations.