John Ferguson and Tony Shaw need no introduction to Acorn User readers and this latest book is written in their usual thorough but easy-going style. Basically a rewrite of their book for the Beeb, it is aimed squarely at the newcomer to machine code.

The first two chapters explain how the computer works at machine-level, and the next three introduce the asssembler at its simplest level, followed by a summary. Chapters 6-10 go on to more complex functions, again followed by a summary. Chapter 11 brings the whole thing together, chapter 12 deals with interrupt handling, and chapter 13 rounds off by showing the stages in developing a complete program - a text editor, in this case. The book ends with set of useful appendices and an index. Throughout there are example programs, diagrams and cartoons.

The book contains one or two small mistakes, but nothing worth worrying about. Two things I would like to have seen are a note about 'modulus' effects, when indexing with the X and Y registers, and a note about the 'bug' common to all 6502 processors, which can cause indirect jumps to be incorrectly handled. These are, however, minor criticisms and I commend this book to anyone (not just Electron users) who wants an easy introduction to machine code.