A distance line is an item of diving equipment used by SCUBA divers as a means of returning to a safe starting point in conditions of low visibilty or where pilotage is difficult. They are often used in cave diving and wreck diving where the diver must return to open water after a penetration when it may be difficult to discern the return route.
50 metres of line on a reel
Distance lines are often wound on to a spool or a reel. Typically 50 metres / 165 feet of thin polypropylene line can be stored on a single reel, which has usually a locking mechanism and a winding handle. Lines are also used to deploy surface marker buoys and decompression buoys.