Since J W Norie published the first edition of this famous set of mathematical tables in 1803, the book has become – and remained - a bestseller. Despite developments in electronic navigation it remains an essential requirement for anyone learning and practising astro-navigation. Since the commissioning of the Global Positioning System (GPS), its proven accuracy and reliability in all weather conditions have resulted in confidence and almost unquestioning dependence on its ability to provide a vessel’s position, course and speed. Because of this, some seafarers feel that the traditional navigational methods are obsolete. However, the marine environment of heavy vibration, stormy seas, salt-laden spray and wide temperature variations can easily damage electronic equipment. No prudent seafarer would proceed on an ocean passage without a reliable navigational back-up. Because of the difficulties which may be experienced if GPS should be unavailable, the book gives an Explanation in the form of a detailed step-by-step description, by means of worked examples, of the different methods of calculating the ship’s position using the tables and/or a pocket calculator. Since the last update in 2007, the editor, George Blance, has made many changes- new tables have been included and obsolete ones deleted to conform with changing techniques of navigation, with the aim of improving the accuracy of the calculated position and reducing the tedium of the calculation. The section Seaports of the World has again been extensively updated and restructured with several hundred additional ports. The ports are listed geographically and also indexed alphabetically to aid identification.