1. R. Homer, Fitzgerald, The odyssey, 1990.
2. Astronomy and Navigation in Polynesia and Micronesia;Åkerblom,1968
3. The Earth’s Magnetic Field: Its History, Origin and Planetary Perspective;Merrill,1983
4. E. Britannica, vol. XXIV, 11th ed. Cambridge, UK: CUP 94.
5. Mobile robot positioning: sensors and techniques;Borenstein;J. Rob. Syst.,1997