With this tool selected you can click out a polygon to define the region of interest (i.e. the area to be counted) on each grain in turn. Alternatively if the region of interest is the whole area then right click with the cursor in the image area and select the Default ROI on all grains option. You should ensure that the ROI is always one fission fragment range (~8 µm) in from an outside edge of any grain. This will add a ROI which is set in from the edge of the image by a present amount, which is set using the Set default ROI inset option in the same pop-up menu which opens the Analysis Settings window. When the ROI tool is active you can adjust the area by dragging any of the vertices, adding or deleting vertices by double-clicking on a line, or using the right-click pop-up menu anywhere on an edge of the ROI. perYou can define multiple ROIs in a grain, up to the user-defined limit set in the Analysis Settings window.