Microsoft Project 2013: The Missing Manual

Understanding Duration, Work, and Units

Assigning one resource to a task and obtaining the results you want is relatively easy, but modifying existing assignments can be a puzzle. For example, if you assign two more people to attend a meeting in Project, the program makes the meeting shorter (as if that would happen) instead of adding those people’s time to the total hours. Understanding how duration, work, and units interact is the first step toward getting the right assignment results the first time—and every time.

Project has built-in rules about which values it changes. To give you a fighting chance, it also offers features that let you control which variables hold steady and which ones change. Task duration, work (think person-hours), and resource units (the proportion of time that resources work on a task) are like three people playing Twister—when one of these variables changes, the others must change to keep things balanced.

When you first assign resources to a task, the task’s duration is inextricably connected to the work and units of that resource assignment. The formula is simple no matter which variable you want to calculate. The basic algebra you learned in high school is all you need: Duration = Work ÷ Units, so Work = Duration x Units. Project calculates one of these three variables when you set the other two, as you can see in Figure 9-15:

• Work = Duration x Units. If you estimate task duration and specify the units that a resource devotes to that task, then Project ...