The "Golden Canon" of book-page design is based upon a set of geometric proportion rules (unrelated to the golden ratio) that plausibly guided some medieval scribes and early-modern printers as they planned their page layouts. Using photographs of these centuries-old manuscripts and printed books, along with the Geometer's Sketchpad computer program, we can ascertain the degree to which the golden canon might have been used to place the text area on the pages of any given handwritten or printed book. In many cases, the layouts closely match what the proportional rules predict.