When the applet starts, you see a set of points generated the same way
as the data for assignment 1.
The New button generates a new set of points.
The True button shows the true line that generated the points. Press again to hide the true line.
The Errs button shows or hides the random errors that generated the points. Each point is the true line, plus or minus the random error.
The LS button shows or hides the least squares line through the points.
The Res button shows orhides the residuals, the vertical differences between the points and the least squares line.
The Squ button shows or hides the squares of the residuals. The least squares line minimizes the sum of the areas of these squares.