by arrows, particularly if there are alternatives available which the team does not want to use. To avoid confusing other divers, these temporary markers are removed on the way out. Hybrid markers A hybrid marker, also known as a referencing exit marker or REM, is a more recently developed line marker used as a directional marker by the diver placing it, and seen as a cookie by others. They are rectangular with slots like the arrow and cookie forms for attachment to a line, and have a relatively large blank space on one end to add identification on one side and to write on the other side. Referencing exit markers are asymmetrical so can be used to show the direction which the diver came from. They are personal markers, and should not be used by others to judge the suitability of a route as the practicability of an exit may depend on the size of the diver and the equipment carried. Manufacture Originally hand made from available materials. Commercially marketed line markers are commonly injection-moulded plastic and are available in a few colours. Small variations in size and shape allow personal markers to be identified more easily, and unique markings may be added by the user. See also External links History of line arrows Wilson's Arrow References Navigation Underwater diving safety equipment Caving equipment