9Scientific Advertising is a book written by Claude C Hopkins in 1923 and is cited by many advertising and marketing personalities (such as David Ogilvy, Gary Halbert and Jay Abraham) as a "must-read" book. David Ogilvy is widely quoted as saying that "Nobody, at any level, should be allowed to have anything to do with advertising until he has read this book seven times". The book is cited as being the original description of the process of split testing and of coupon based customer tracking and loyalty schemes. In the book, Hopkins outlines an advertising approach based on testing and measuring. In this way losses from unsuccessful ads are kept to a safe level while gains from profitable ads are multiplied. Or, as Hopkins wrote, the advertiser is "playing on the safe side of a hundred to one shot". "The book also contains information on how to write advertising that sells: Salesmanship in print."