This is the experiment you just ran. You should also see a blue curve. This is the analytic result given above. As discussed above, the more configurations you generate the closer you will get to the theoretical curve. Now let's fill out the whole curve. if you click on auto the applet will automatically cycle through various probabilities and plot the results.
Exercise Increase the number of configurations and generate a new curve.
It should be more accurate. Exercise Think of a method to associate an error with each point you calculate. In fact we are often interested in the bulk limit where the system size goes to infinity. To do this select 4x4 in the top pull-down menu. Compare the 2x2 and 4x4 plots.