- A PERT calculation produces an Expected Time (Te)
- Expected Time, or 'Mean' (as distinct from average) is a term given to a calculated weighted average of three estimates:
- Optimistic (O), the Most Likely (L) and Pessimistic (P)

- PERT assumes a 'Bell Curve' distribution (so called because of its shape like a bell) in its weighting formula
- Thus: Te = (O+4L+P) 6
- Variance can be calculated from V = (P-O) 2 6
- Standard Deviation (s) is the square root of Variance

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