Why should I do three point estimation and use the PERT forumla?
PERT helps you take uncertainty into account when estimating projects. PERT requires a three point estimate. This means that you estimate the low (optimistic), most likely (realistic) and high (pessimistic) hourly hours for each line item in your estimate.  Simple Estimate  uses the PERT formula to calculate accurate cost estimates. The PERT formula was developed by the US Navy in 1957.