 Click in one of the dark gray margins at either side of the graph to
bring up a "guide line" which you can drag
out across the graph. A shaded area is marked out behind the
guide, and the window displays the probability of the distribution
falling in this area.
 You can draw out a second guide, to mark out twosided regions.
 Click and drag to move the guide lines once you have laid them out. Drop
a line back in the gray margin area to remove it from the screen.
 The graph of the normal distribution is shown for values of x
between xMax and xMin, which can be changed by typing in the textboxes.
 Initially, figures are given for a distribution with mean 0 and
standard deviation 1. You can changes these values by typing in
the appropriate boxes.
 You can enter numerical values for the guide positions by clicking the
"Set range..." button. Enter the values of the probability range in the
fields of the popup panel, and click the OK button (the green check) or
dismiss the panel with the Cancel button (the red cross).
