One of the major sources for the biography was Leonardo’s astonishing notebook. A table of contents of the notebooks would be a small book in itself, as there are more than 7,200 pages crammed with notes and scribbles: “math calculations, sketches of his devilish young boyfriend, birds, flying machines, theater props, eddies of water, blood valves, grotesque heads, angels, siphons, plant stems, sawed-apart skulls, tips for painters, notes on the eye and optics, weapons of war, fables, riddles, and studies for paintings. The cross-disciplinary brilliance whirls across every page, providing a delightful display of a mind dancing with nature.”

It is clear from Isaacson’s description that Leonardo was an obsessive-compulsive personality, “... evident not in each measurement but in the staggering accumulation of them. He goes on and on, relentlessly. We can picture him in his studio, as he made his models move ...When a man kneels down, he will diminish by the fourth part of his height ... When a heel is raised, the tendon and ankle get closer to each other by a finger’s breadth ... When a man sits down, the distance from his seat to the top part of his head will be half of his height plus the thickness and length of the testicles.”