These functions plot a distribution, then create a Tk slider box that
allows you to adjust the parameters of the distribution to see how the
curve changes.
Check boxes are available in some cases to also show reference
distributions (normal and poisson for the binomial, exponential and
chi-squared for gamma, and normal for t). The exponential and
chi-squared distributions are those with the same mean as the plotted
gamma.
If you change the plotting
ranges then you need to click on the 'refresh' button to update the plot.