a compact , lightweight , self - contained rappel apparatus by which a person such as a parachuting smoke jumper , aviator , or other person may safely descend a line or rope from a tree canopy or other high perch to the ground or a lower elevation . the invention is designed for one - handed use with a preferred figure 8 system of descent line reeving around and about the top pipe and bottom pipe of the descender that results in multiple frictional line - to - line contact points as the line crosses itself in each figure 8 wrap in the area between the top pipe and bottom pipe .