The project manager must keep in mind the difference between effort and duration . Duration is the amount of time that elapses between the time the task is started and the time it is completed, measured in hours (or days, weeks, etc.). It does not take into account the number of people performing the task. Effort is measured in person-hours (or person-days, person-weeks, etc.), and represents the total number of hours that each person spent working on the task.
Nice differentiation between effort & duration.
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