For a friend who is a free-lance designer and has to do everything herself:

We used to have specialist that we could ask for advice, rely on for help and also blame for things that went wrong during the production process. These days, graphic designers have to be their own typesetters, reproduction photographers and print buyers. There are websites, help pages, blogs and numerous articles in trade magazines. But if you only want one reference that explains why things need to be a certain way, this book is all you’ll ever need. From typographic detail to color spaces, from paper types and sizes to image editing, it’s all here. Described in incredible but useful detail (the author is a German compositor) and illustrated in a way that coincides with what you see on your screen as you work.

As the U. S. is one of the very few countries left in the world that still doesn’t use the metric system, the book includes American sizes and measures along with the metric figures, making it also useful as a reference for conversion between the two.

If you only want one reference while you work, this is it.

Full disclosure: the book was translated from German into English by my son, Dylan Spiekermann, who has an English mother and lives in London. I helped with technical consultation for the English-language edition.