The invention relates to a method and a computer for coordinating an electronic credit application between an Internet user and a plurality of lending institutions via the Internet. The spiral pitch of a spiral part in a vicinity of one of the ends and an adjacent spiral part in the direction of the axis is set larger than the spiral pitch of other adjacent spiral parts, to widen a gap between the one end and the adjacent spiral part. Accordingly, the projection system adopting an image display device as a liquid crystal device provides a remarkably enhanced contrast enhancement effect. Furthermore, the polyurethane ballast layer can keep the polyurethane foam filled in the ballasts layer away from water in the outside environment to avoid hydrolysis.