The Integration tool allows you to calculate the integral over a selected region. To use it, first select nodes, edges, faces, or elements. Then, activate the Integration tool from the Post/Integrate menu. A window appears with a graph that represents the integral of the selected region as a function of time. Depending on the selection, the graph represents different things. For nodes, it is the sum of the values all the selected nodes, for edges it is the line integral, for faces it is the surface integral of the selected surface, and for elements it is the volume integral over the volume of the selected elements. The Save button saves the results to a text file and the Clipboard button copies the data to the clipboard.