Dry cavers were using directional markers long before there were any
cave divers. The early cave divers in Florida saw the benefit of these
markers, and Lewis Holzendorf came up with the idea of folding a
triangle of tape around the line to form an arrow. These tape arrows
were called "Dorf" markers, in Lewis' honor. Today, cave and wreck
penetration divers from all around the world use line arrows to mark the
direction of the closest exit.