Whenever you change the scale to look at a graph in greater detail or from farther back, or you shift the range of the axes so that the graph you just drew will be centered, the graphs on screen must be recalculated over the new range.
As its name suggests, AutoRedraw will redraw the equations on screen automatically when you change the scale or range. If your machine is an older, slower one and you don't want to wait for the graphs to be redrawn, you can abort the redraw by pressing ESC twice.
You can limit the number of equations AutoRedraw draws by reducing the number on the line
AutoRedraw On--Draw Last ___ equations
in the Options Settings dialog box. This can be anything from 1 to 999, the maximum number of graphs. If this number is greater than the number of equations in memory, all graphs on screen will be redrawn. The default is 25.
Finally, you can turn off AutoRedraw completely by selecting AutoRedraw under the Options menu.