Using the Probability 

This
feature allows you to see the Bell Curve in relation to your trade. To
open a probability graph, click the calculate button with your trade information
in the option matrix, then click the Probability Graph button. This is an example of the probability graph of an index credit spread. While the graph above looks like a normal symmetrical
bell curve, the graph below does not. This is because of a log normal distribution. i.e. the chances of the
asset doubling in price are equal to the chances of the asset being cut in
half. When displaying the probability on a chart with the prices, it can
make the chart look a little funny when there is a lot of time before the
options expire The less time before expiration the more normal the curve appears
to be.

