We never saved the Formula cell. Try adding it to the Preferences panel and saving it.

Instead of saving them in the Preferences panel, arrange for the GraphPaper application to automatically remember the values for xmin, xmax, ymin, ymax, and xstep as they are entered on the GraphPaper main window. What are the advantages and disadvantages of this approach over using the Preferences panel?

Further modify the Preferences implementation so that the color preference is set when a new color is dragged in. Does this make the system easier or harder to use?

Should there even be a Preferences panel? Implement the application without it. Discuss the advantages and disadvantages of having a Preferences panel.