Every time you type in an equation, the character string you typed and the program's internal representation of that equation get stored in the redraw queue. From this queue, or list, you can call up any of the equations in your current graph document to edit or draw again. The equations in the queue are stored in an order that puts the most-recently-used at the beginning and the least-recently-used at the end. Hopefully, when the queue fills up, the equations that are bumped off the queue at the end will be the ones you won't miss very much.
The screen clears whenever you execute a Range or Scale command. If you execute either of these functions or clear the screen accidentally with the Clear menu option, you can redraw the last equation (if AutoRedraw hasn't already) by selecting Last Graph from the Redraw menu, or you can redraw all of the equations in the queue using the Redraw All menu option or button. Note that the redraw all function does not care which graphs were on the screen before it was cleared; it just redraws all the graphs in the redraw queue that are not currently on the screen. If you cleared the screen manually, and have not changed the size of the grid before you choose Redraw All, Graphmatica will detect which graphs have already been calculated using that grid and redraw them without recalculating their points (this is faster than plotting the graph from scratch).
You can scroll through every equation you have entered into the redraw queue using the combo box at the top of the screen. When you select an equation using the arrow keys or mouse, Graphmatica displays its current status (on or off screen) and the text of the equation in the same color the graph was drawn in at the bottom of the screen in the status bar. Press the down arrow key or pull down the listbox with the mouse to scroll back one equation. Press the up arrow key or button to scroll back up the list if you want to. When you have found the equation you want, press enter or click on it and press enter or click the Graph button (do not modify the equation) and the graph will be redrawn. Afterwards, the equation will be displayed for editing, except now it is at the head of the queue.