This calculator uses the following formulas:
Expected Time = (Optimistic + Most Likely * 4 + Pessimistic) / 6
Variance = ((Pessimistic - Optimistic) / 6)2
Please be sure to use the same unit for all of the times. For example if you believe that an optimistic time is 12 hours while a most likely number is 1 day then you need to be sure to enter it as ".5" and then "1", making them both days. It does not matter what unit that you use as long as you use the same one through out. Also what ever unit you use in the data entry is the same unit that will come out in the resuls.