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.
Limited quantities currently available in green, blue, and glow-in-the-dark, which have been discontinued.
Also available in white.