The Van de Graaf canon is used in book design to divide a page in pleasing proportions. This canon is also known as the "secret canon" used in many medieval manuscripts and incunabula. The page proportions vary, but most commonly used is the 2:3 proportion. In this canon the text area and page size are of same proportions, and the height of the text area equals the page width.
Popularized by Jan Tschichold in his book The Form of the Book in 1975.
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