In the graph controls Options box you can enable or disable the Crosshair or the Symbols. When Crosshair is enabled (checked) the crosshair and its readout are shown on the graph. Click on the graph to move the crosshair to that location. Click within the area of the crosshair itself to move the crosshair one pixel at a time toward the mouse cursor. The crosshair's readout gives the exact location of the crosshair's position on the graph.
When Symbols is enabled (checked), the traces are plotted with symbols over the lines. The symbols allow the plots to be distinguished from each other when printing to a black on white printer.