Read for both personal and professional interest, this comprehensive large-format hardback book tells the whole story of railway signalling, from the earliest days of hand-signalled, time-interval working right through to todays's Digital Railway, with extensive automation. It's designed for reading by those without a prior background in the subject, and it was pitched at an ideal level for what I needed. It doesn't go into detail on exactly how everything works, but it does explain well how things developed and why, and that was just what I needed. Plenty of photos and diagrams to back everything up, and clear text with terms well-explained. A useful addition to my reference collection.