When you assign or remove people from a task (task: An activity that has a beginning and an end. Project plans are made up of tasks.), Microsoft Office Project 2003 lengthens or shortens the duration (duration: The total span of active working time that is required to complete a task. This is generally the amount of working time from the start to finish of a task, as defined by the project and resource calendar.) of the task based on the number of resources (resources: The people, equipment, and material that are used to complete tasks in a project.) assigned to it, but it does not change the total work (work: For tasks, the total labor required to complete a task. For assignments, the amount of work to which a resource is assigned. For resources, the total amount of work to which a resource is assigned for all tasks. Work is different from task duration.) for the task. This is called effort-driven scheduling (effort-driven scheduling: The default method of scheduling in Project; the duration of a task shortens or lengthens as resources are added or removed from a task, while the amount of effort necessary to complete a task remains unchanged.) and is the default Project uses when you assign resources to tasks.
As resources are added to a task, the total work on the task stays the same. However, the amount of work distributed to the resources assigned to the task changes.
Effort-driven scheduling only takes effect when resources are added to or removed from a task. Effort-driven calculation rules are not applied when you change work, duration, and unit (units: The quantity of a resource assigned to a task. The maximum units is the maximum number of units available for the resource. For example, if you have three plumbers, the maximum units is 300 percent or three plumbers working full-time.) values for resources already assigned to a task.
When working with effort-driven scheduling, keep the following in mind: