"'Archivists have been looking for a copy of Diagramma for years. But between the Vatican burnings and the booklet's low permanence rating, the booklet has disappeared off the face of the earth.' 'Permanence rating?' 'Durability. Archivists rate documents one through ten for their structural integrity.Diagramma was printed on sedge papyrus. It's like tissue paper. Life span of no more than a century.'" - 'Angels and Demons', Dan Brown.