The Golden Ratio is key to aesthetic design. Although many designers today don't rely much on this concept, but it brings finesse and precise balance to logo designs.
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The timeless CN mark was designed by Allan Flemming in 1959. The story goes that Fleming came up with the design while traveling on a New York-bound airplane, where he sketched the idea on a cocktail napkin. Graham Smith put together a great write-up on the history of the logo, with some links to more resourceful information.