This function determines the confidence inverval around a mean, given the standard deviation and number of tests.
The case menu is used to set an appropriate equation for the information given. Use Case 1 if you know the standard deviation. Use Case 2 if you know only the sample standard deviation, and n is greater than 30. Use Case 3 if you do not know the standard deviation and n is less than 30.
Alpha is 100% - the confidence level (i.e. for a 90% CI, alpha = .10).
x bar is the sample mean.
Sigma is the standard deviation. This is used for the sample standard deviation for case 2, and is left blank for case 3.