Rogue Trader 2015: Halcyon Rising
Charts plotting routes through the Immaterium are not at all like conventional charts of real space. They exist as abstract concepts, communicated between Navigators by psychic means. The information could be stored in a roll of psychically charged parchment, a staff impregnated with the navigational lore of the family, or a servo-skull fashioned from a revered ancestor. A Navigator can mentally retrieve this information by touch, often after reciting a secret mantra, and can instinctively hone in on the particular lore he is seeking, the knowledge of the Warp route flooding into his mind. To prevent rivals accessing the charts, the information is disguised by impenetrable ciphers. A Navigator can automatically “read” a chart prepared by his own House. However, to crack an unfamiliar cipher, the Navigator must pass a Very Hard (–30) Forbidden Lore (Navigators) Test.