The book by the famous French author Patrick Guell will reveal to you the secrets of magnetic cards, these convenient and reliable means that make it possible to easily and simply solve many technical problems - payment, access, control. The publication contains everything you need so that you can study the principles of recording , reading, encoding and decoding magnetic card information; descriptions of simple devices will allow you to make them yourself. Many different programs will provide powerful tools for research and experimentation with maps using a computer. After reading this book, you will learn to confidently manipulate map information, recording any data on them, in other words, you will be able to penetrate the “holy of holies” of professionals.