 The Brunswicks tolerated the enormous effort Leibniz devoted to intellectual pursuits unrelated to his duties as a courtier, pursuits such as perfecting calculus, writing about other mathematics, logic, physics, and philosophy, and keeping up a vast correspondence.He began working on calculus in 1674; the earliest evidence of its use in his surviving notebooks is 1675.By 1677 he had a coherent system in hand, but did not publish it until 1684.