A basis of duration records why an activity takes as long as the schedule says. Without one, a review is opinion against opinion. With one, you can discuss the quantity, the rate or the crew, which are the things that can really change.
The standard formulas
PF is the productivity factor. 1 means standard norms, and above 1 means slower, for example because of congested access or weather.
- From manhours: Duration = Manhours x PF / (Crew size x Hours per shift x Shifts per day).
- From quantity and unit rate: Manhours = Quantity x Unit rate, then the formula above.
- From quantity and output: Duration = Quantity x PF / (Crews x Output per crew per shift x Shifts per day).
Worked example
These figures are examples only. 480 manhours at a PF of 1.1, with a crew of 6 working one 8-hour shift a day: 480 x 1.1 / (6 x 8 x 1) = 11 days.
What makes it hold up
- Quantities that trace back to the estimate.
- Rates with a source: your own records first, published norms second.
- A crew size the site can really fit and hire.
- A clear reason for every PF other than 1.
Is your own schedule healthy?
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