Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. In mathematics, specifically in integral calculus, the rectangle method (also called the midpoint or mid-ordinate rule) computes an approximation to a definite integral, made by finding the area of a collection of rectangles whose heights are determined by the values of the function. Specifically, the interval (a,b) over which the function is to be integrated is divided into n equal subintervals of length = (b a) / n. The rectangles are then drawn so that either their left or right corners, or the middle of their top line lies on the graph of the function, with bases running along the x-axis.