end and a clip at the other, but other methods are also used. Reasonable security and easy access are all that is required. Directional markers Line arrows are used to indicate the direction along the line to the nearest air source. In cave systems with only one opening, line arrows will always indicate the route back to the entry, but in cave systems with multiple openings, they may not point to the entry used by the dive team, and in some cases this may not be a usable exit. Some popular cave diving systems have permanent line arrows at regular intervals pointing to the nearest exit, and may be marked with a distance to the exit. Permanent arrows may also be used to identify secondary passages and midpoints in a cave. Line arrows are placed to help the divers to establish the direction they come from, when they later need to find the way out, but should not alter the general navigation information of the system, so line arrows are added only where they cannot cause other groups to become confused about the direction to the nearest air source. An arrow would be added at the point of attachment of a reel line when tying off to explore new areas, and may be removed after return and removal of the temporary line. If the place is to be marked for future reference, the arrow may be left in place. Non-directional markers The original non-directional markers in cave diving were clothes pegs, but the circular plastic "cookies" were developed later, based on the successful line-arrow design, and are more secure when placed on a guideline. They can be used to mark reference points, to distinguish lines at an intersection, or can be placed by each member of a team on a jump or gap line to identify who is still on the line if the team gets separated. As they are commonly used to identify the presence of a diver, they generally have some kind of personal identification, such as initials or drawings and may have notches, or holes added so they can be identified by feel. A non-directional marker indicates the presence of a diver or team beyond a point and is mainly useful for that team. They may be used to indicate the direction the team came from and intend to exit by when the intersection is already marked