one-trick pony
This app does what it says, it returns the value of the area under the Gaussian curve from negative infinity to z, for a given mu and sigma. This is a lot handier than looking it up in a table. The values it returns match the values I get from tables, to the same precision (5 digits). The graph is useful for illustrative purposes if the the mean (mu) is close to zero, but there is no way to re-scale the graph if the mean is, say, 100. Not a problem, we really only want the numerical value. What would make this a great app (that I would pay for): 1) Add the ability to calculate the area under the curve from z1 to z2, not just the tail. 2) Add the ability to enter a normalized value (z-mu)/sigma rather than three separate values. 3) Add the ability to switch from Gaussian to Q and erf functions. It's really all the same problem, but sometimes one approach is better than others. 4) Display the Gaussian, erf, and Q function formulas for reference. 5) Make the graph more flexible, illustrative, useful. 6) Add other common probability densities and calculate the statistics for them. Still, it's great for free!
