The sheath for receiving a head-rest branch includes at least one wedge disposed in a window formed in a wall of the sheath and adapted to be disposed between the bushing and the branch, said wedge having a thickness greater than that of said wall so that, when the sheath is housed in the bushing and the branch is received in the sheath, the wedge is compressed between the bushing and the branch. The presence information often indicates the status of a user in an instant messaging environment. The method and system described herein uses a sliding variance across the entire cable length. The surface of the plurality of pages that accepts dry-erase markings may also include one or more dry-erase sections configured to aid players in tracking game progress, such as on a dry-erase scoreboard. One or more portions of the computer-based material are determined to be of interest to a user. A two-electrode element is formed by using the horizontal charge transfer channel, barrier region and drain region.