stick charts by curved sticks and threads. Rilib swells Rilib swells are the strongest of the four ocean swells and were referred to as "backbone" swells. They are generated by the northeast trade winds and are present during the entire year, even when they do not penetrate as far south as the Marshall Islands. Marshallese considered the rilib swells to come from the east, even though the angle of the winds as well as the impact of the ocean currents varied the swell direction. Kaelib swells The kaelib swell is weaker than the rilib and could only be detected by knowledgeable persons, but it is also present year round. Bungdockerik swells The bungdockerik is present year round as well and arises in the southwest. This swell is often as strong as the rilib in the southern islands. Bundockeing swells The bundockeing swell is the weakest of the four swells, and is mainly felt in the northern islands. Stick chart categories The stick charts typically fall into three main categories: mattang, meddo (or medo), and rebbelib (or rebbelith). Mattang charts The mattang stick chart was an abstract chart used for instruction and for teaching principles of reading how islands disrupt swells. Meddo charts The meddo chart showed actual islands and their relative or exact positions. Meddo charts also showed the direction of main deep ocean swells, the way the swells curved around specific islands and intersected with one another, and distance from a canoe at which an island could be detected. The meddo chart portrayed only a section of one of the two main island chains. Rebbelib charts Rebbelib charts portrayed the same information as a meddo chart, but the difference lies in inclusiveness of the islands. Rebbelib charts, unlike meddo charts, included all or most of one or both chains of islands. Knowledge transfer Stick charts were not made and used by all Marshall Islanders. Only a select few rulers knew the method of making the maps, and the knowledge was only passed on from father to son. So that others could utilize the expertise of the navigator, fifteen or more canoes sailed together in a squadron, accompanied by a leader pilot skilled in use of the charts. It was not until 1862 that this unique piloting system was revealed in a public notice prepared by a resident missionary. It was not until the 1890s that it was comprehensively described