• The motion of specific stars, and where they would rise and set on the horizon of the ocean
These sets of information were kept as guild secrets. Generally, each island maintained a guild, or group, of master navigators who had very high status. In times of famine or difficulty, only they could trade for aid or evacuate people. The guild secrets were almost lost. Fortunately, one of the last living navigators taught them to a professional small-boat captain so that he could write them down. The captain recorded these secrets in book form, creating an early navigator's manual.