A golf club head cover includes a bottom wall and a pair of side walls extending from the bottom wall to form a compartment for containing a golf club head. The upper electrode plate comprises a flat vibration area and a surrounding flexible area connected thereto. The system then recursively traverses referents of the root objects which are MS objects and while doing so, marks referents of the traversed MS objects. A candidate NMR for a mobile device may be received, and the candidate NMR may then be associated with a selected cluster of NMRs. The cryptographic structure can be built only by whoever emits the card or an agent thereof. According to the invention, the input shaft which is rotatably mounted in the region of a first end wall is guided up to the second end wall located in opposition to the first end wall and is rotatably mounted there indirectly via the output shafts which are also rotatably mounted in the region of the second end wall.