For those who are serious in their optics, this free handbook on retical patterns is available as a free ebook download courtesy of Gun Digest... "This handy 100-page reference contains diagrams of tactical reticles from all the major optics manufacturers. D. Andrew Kopas shares the digital handbook with members of gundigest.com and scout/snipers in all branches of the armed forces, police marksmanship units and civilian long-distance shooting disciplines.