This function returns a factor. (Quality Control D3 Factor)
It determines the 3-sigma lower control limit for R charts (Range of Sample Charts) from the average range when the sample size (or subgroup size) n is given.
The Lower Control Limit for R = (factor)*(Average Range).
The calculations for the factors are based on the normal distribution.
double QCD3(int n)
Returns Quality Control D3 Factor.
QCD3(11) = ; //returns 0.256, the factor for a sample size of 11