Quote:
Originally Posted by sticky
What I dont understand is " graph is drawn in a sigmascale for the yaxis"".

It is easy to understand by analogy. Suppose you have some variable that has an exponential behavior (for example any biological effect that is measured by luminescence, e.g. gene expression). To make it look linear, you change the plot to have yaxis transformed by the function
inverse to exponent. What function is this? It is log().
Same here. CDF is known to have a wavelike, monotone function, usually denoted 𝛷() that describes it (when underlying distribution is normal). How do you transform yaxis? You apply the inverse function 𝛷
^{1}(). It doesn't have an analytic expression but that doesn't matter  you can use a function that is indistinguishable from precise function, within pixels on your screen  you will not know the difference. So that's what programs like SigmaPlot do. It is rather simple.