'Calculus is a central branch of mathematics, developed from algebra and geometry. It is built around two major complementary ideas, both of which have clear geometric meaning: rate of change and area. To get beyond the simplest cases of these notions, such as constant speed or constant acceleration, or polygonal areas, mathematicians have come to rely critically on the concept of limits. Therefore calculus depends not only on algebraic and geometric thinking, but on further ideas that were developed systematically from the seventeenth century onwards.'