A remote-controlled motor-driven drum is provided to wind and unwind a cord which holds a self-balancing sign carrier. Specifically, a detection and tracking method which precisely describes a handwriting sample as a plurality of features which become indicators of a medical disorder affecting fine motor skills. Compressing prefixes of names in the hierarchy list is performed by comparing a previous entry to a current entry. Thus, a correspondent node, though it does not recognize the IP address of the mobile station, can access the mobile station using the domain name.