Once you have entered an equation, you can easily pull it up and manipulate it again at any time. To select an equation in the redraw queue, do one of the following:
Using either the down arrow key or the mouse, highlight the equation in the redraw queue combo-box. You can also select the equation by retyping it in the edit field, but it must match exactly.
If the equation's graph is currently on screen and is not completely covered by another graph, just click on the curve; the corresponding equation will automatically be selected in the listbox (This works for all graphs except slope-fields. However, you must click on the curve, even if the graph is an inequality.)