This book is a compilation of all the formulae that a mariner is commonly called upon to use but the exact workings of which he has perhaps forgotten. For each subject category, the author states the basic parameters in narrative form, often including a figure, graph, chart, diagram, or table, and then provides accompanying equations and their amplifications. Although some formulae that are simpler in format are propounded in other texts, many of those formulae lead to confusion in that 'special rules' must be applied to them in order to obtain a correct answer. However, the rules applied to the formulae in this book work for all problems. In a great circle sailing situation, for example, the fact of whether the vertex is ahead of you or behind you does not matter—if you apply the rule(s) given in this book, you will get the correct answer. Another important feature of the book is its devotion of over ten pages of material to the international system of units (S.I.)