Architectural guidebooks tend to be a constant companion when travelling round a city- who designed that, when was it built, finding out about the back story, questions that need instant answers. The recently launched App for iPhone and iPad Edifice London maybe makes the guide book redundant as it's so immediate. Walking down the street, you can, with luck, immediately pinpoint the building you're looking at, or one in the next street. Beautifully produced, good pictures, well written and well informed texts largely by the App's originator Sandy McCreery. It's a work in process so not everything is on yet, but well worth anyone buying for an amazingly modest fee.