This aid involves work on the horizontal plane. The elbow bends and extends to reach the curves on the flexible element. Inclined radial / ulnar movements are required to get past them. Positioning on a vertical panel: in this case the instrument lies on the vertical plane.
This instrument is therefore similar to the vertical spiral, but differs in that positioning it at various heights and working in an upright position, obliges the subject to achieve greater bending and extension of the arm.