an input peripheral for a computer or the like , includes a moving portion handled by the operator and fitted with electrical sensors suitable for generating electrical signals for the computer in response to movements imposed on the moving portion by the operator . the moving portion includes a shell connected to a stationary base via a linkage arranged to allow any movement of the shell relative to the base with the exception of movement in a direction substantially perpendicular to a bearing plane of the base , the moving portion further including a hull that is entrained by the shell and that includes a side wall extending so as to prevent any intrusion under the shell regardless of its position .