A mirror screw consists of mirrors arranged one above the other on one axle, which are positioned on a slight angle from each other. Upon rotation, each mirror provides one image line. The mirror screw can be manufactured with high precision. In 1931, TeKaDe began to build television receivers with mirror screws. Up to 180 lines were possible, with the image being almost as high as the screw. The light output was excellent, so the picture was both very bright and sharp.