Every title different, every cover the same.

Penguin’s covers were already divided into three horizontal bands when Jan Tschichold arrived in 1947. Edward Young had drawn that grid in 1935: colour at the top and bottom, the author and title in the white band between, and one colour for each kind of book, orange for fiction.

Between 1947 and 1949 Tschichold refined the system rather than replacing it. He redrew the penguin, reset the covers in Gill Sans with careful spacing, and wrote the Penguin Composition Rules, four pages of instructions for every editor and compositor. Some five hundred books passed through his hands.

No. 616, The Picture of Dorian Gray from 1949, is one of those covers, and the red lines on the plate fall exactly on its band edges. Change the author, the title and even the colour, and the cover still reads as Penguin, because the structure stays put.