The integral function calculates the area under a segment of the graph. The selected area is filled on the graph and a helper object displays the numeric result. The integral is calculated using the trapezoid rule.

Click and drag the mouse across the segment that you want to integrate. The shaded area marks the beginning and end of the range. The direction you move the mouse is not significant. If you don't select a range, the curve will be fitted to the entire range of data displayed in the graph

Choose the integral function either by clicking the Integral button  on the toolbar or by selecting the Integral option from the Analyze Menu. You can click and drag the brackets and the integral will update automatically. To remove the integral from the graph, click the close box in the upper corner of the integral helper object. To edit the integral's properties, double-click the helper object. The Integral Options dialog box will appear.