This command should never have to be used. But some OpenGL drivers don't do a very good job at refreshing the view of the graph. So if for some reason your display becomes corrupted, you can refresh it by right clicking on the graph and choosing Re-Compute All Equations. This will tell GraphCalc to redraw the view from scratch hopefully fixing your display problem. If your display becomes corrupted often, you should look into getting updated video drivers from your video card manufacturer.