In cave (and occasionally wreck) diving, line markers are used for orientation. Directional markers (commonly arrows) point the way to an exit (although no permanent guideline must exist); non-directional markers ("cookies") are purely personal markers that mark specific spots, or the direction of one's own exit at line intersections / T's. One important reason to be adequately trained before cave diving is that incorrect marking can confuse and fatally endanger not only oneself, but also other divers.
The line arrow was invented by Lewis Holzendorf and developed by Forrest Wilson at the Cave diving NSS workshop, inspired by Sheck Exley and other cave diving pioneers, and later, a few hundreds of the handmade were sold through Branford Dive Center in North Florida. Soon they became very popular and today are commonly used by underwater cave explorers.
Famous quotes containing the words line and/or marker:
“When I had mapped the pond ... I laid a rule on the map lengthwise, and then breadthwise, and found, to my surprise, that the line of greatest length intersected the line of greatest breadth exactly at the point of greatest depth.”
—Henry David Thoreau (1817–1862)
“Personal change, growth, development, identity formation—these tasks that once were thought to belong to childhood and adolescence alone now are recognized as part of adult life as well. Gone is the belief that adulthood is, or ought to be, a time of internal peace and comfort, that growing pains belong only to the young; gone the belief that these are marker events—a job, a mate, a child—through which we will pass into a life of relative ease.”
—Lillian Breslow Rubin (20th century)