Here is a basic, beginner's book, introducing the tyro to the tools, the vocabulary, and the techniques of celestial navigation. Among the recommended tools are the H.O. 249 tables, the most widely used among amateur navigators at sea, because of their simplicity.If you can read, add and subtract, understand angles, and use a protractor, you can learn to navigate in your armchair or at sea from Celestial Navigation by H.O. 249.