'Nothing under P for puncture, T for tyre or even W for wheel. By scanning the manual alphabetically, I eventually found it under I: "If you have a puncture".'
(Comment from a car owner thwarted by an unhelpful index.)
As this quote shows, the indexes to user manuals are sometimes among the most unusable in the world, but it needn't be like that. This series of articles by Bill Johncocks, first published in The Communicator, the quarterly journal of the Institute of Scientific and Technical Communicators (ISTC), explains why indexes to user manuals so often fail their users. An excellent introduction to indexing skills for technical authors, it will also help them to avoid the most common pitfalls.
The Society of Indexers is grateful to Bill Johncocks and the editor of The Communicator for permission to reproduce these articles.