2023 Reprint of the 1930 Edition. Full facsimile of the original edition and not reproduced with Optical Recognition Software. The present manual is intended to supply in a uniform presentation an account of the history, principles, and practical uses of the slide rule. Among its specific aims are: to show the unity of the principle of operation of all slide rules, to explain this principle in a manner which shall be easily understood, to give in clear and simple language explicit and inclusive instructions for the use of all the standard forms, and to supply a fairly complete account of the history of the slide rule and a description of the more usual of the special forms of the rule.