This book is an account of how I addressed the need for a smartphone app that would allow someone with Type 1 diabetes to self-manage their condition.

Its presentation highlights the major features of the app’s interface design. They include the selection of metaphors appropriate to a user’s need to form a mental model of the app; the importance of visible context; the benefits of consistency; and considerations of a user’s cognitive and perceptual abilities. The latter is a key feature of the book.

But the book is also about the design process, and especially about the...