Select File - Add to Graph to add another project to a graph tab. You may open a browse window which allows you to select a project or select a project from the recently used list. You may also select a graph file (.sgrx) that you previously created using the File - Save command or a data output file.
An added project displays the same measurements that are being used in the existing plot.
An added graph file replaces the existing plot, but any projects present before the Add to Graph command are still available to be added to the plot.