The Golden Canon of page design was officially named by John Tschichold in 1953. As pictured in the GIF above, it involved the matching of diagonals to create a text area that held a 2:3 ratio, and that was oriented to the upper inner corner of the page. This spread of the Valerius maximus provides a real-life example of the Golden Canon, which appeared to be ubiquitous despite the inconsistencies between measuring systems in the medieval world.
Max, Stanley M. “The ‘Golden Canon’ of Book Page Design: A Visual Presentation Using Geometer’s Sketchpad.” Bridges 2012: Mathematics, Music, Art, Architecture, Culture, pp. 417-420. https://archive.bridgesmathart.org/2012/bridges2012-417.pdf