In an axial flow fan motor having openings through which air can flow linearly in the axial direction provided between a plurality of blades which rotate along with the rotation of the motor, the plurality of blades are arranged at different intervals or at equal intervals every other blade circumferentially around the rotation axis of the motor. The support structure, vanes and operating elements are adapted to be wrapped around a roller in the head rail in a retracted position of the covering and unwrapped in an extended position. The collected information is then stored centrally. In a third embodiment, a picture is taken of a large portion of the wire cable using a specialized camera and the image is split up into recurring units of length that correspond to the size of a lay length or a multiple of the lay length and the successive units of length are compared and inspected for changes in the image.