When people stumble in their use of Microsoft Project, frequently the problem stems from a lack of understanding of how task types work. If you understand that, then Project can become the most powerful weapon in your project management arsenal. In this article I explain the basics of task types.

For each task in your project, you must set three task type choices:

• Fixed Units (Project's default)
• Fixed Work
• Fixed Duration

To understand these, you have to learn the underlying formula used by the scheduling engine:

Duration * Units = Work

Before I explain each aspect of the formula, please note that with this formula, as you change any given component, that will change the other components too. For any tasks, you can choose which piece of the equation Project will calculate by setting the task type.

Duration is the length of a task measured in business or calendar day.

Units is the number of resources assigned to work on a task. For example, if a person is available 10 hours per week (assuming a standard 40-hour week), this represents a quarter of her available time. The Units equal 25 percent.

I should note that in my experience, resources are rarely available a hundred percent of the time unless they work on only a single project.

Work is the amount of effort a resource must expend on a task, usually measured in units such as hours per week. The total work for a task is the sum of all those time units, no matter how many resources are assigned to the task.

Regarding work, there are some tasks that you can add more resources to and the task's duration will decrease. This is called effort-driven scheduling, which is Project's default. The duration of a task will shrink or grow as resources are added or removed, while the amount of total effort expended on that task stays the same.

For example if you have a week long task to test several units, you can decrease the amount of duration by adding more testers. For other tasks, adding resources won't decrease the duration, such as training. No matter how many instructors one assigns to a three-day training course, it will still take three days. Another example is backing up a computer. One person or 10 can back up a computer -- it will still take the same amount of time. Effort-driven scheduling only occurs if you keep this option clicked in the Task Information dialog and you add or remove resources from a task. (Keep in mind that when you add resources to a task, this does cause some increase to the task's duration due to increased communication needs between the resources.)

Here are the steps for selecting a task type for one or more tasks in Project 2007:

1. Open your project plan and select the task or tasks you desire to change. If choosing multiple tasks, you can click and drag for serial tasks or click and Ctrl-click to select non-serial tasks.
2. Select the Task Information button and go to the Advanced tab. If you only select one task, you can double-click anywhere on the task row to open the Task Information dialog box.

Figure 1. The Task Information button

Use the Task type: drop-down menu to select the appropriate task type. Select the Effort Driven checkbox if desired. Note! Most of the time I leave "Effort-driven" unchecked.

As I stated earlier, you must set your task to be one of three types. So how do you know which one to use? Here are some guidelines.

Fixed Units Tasks

Fixed unit tasks means that in the formula Duration * Units = Work the units are fixed. Use Fixed Unit tasks in situations such as:

• When the number of resources you have for the task is the first or main thing you know.
• When you can't get more resources to do the work -- your resources are fixed.
• When you want to change the duration or the work on a task while keeping the number of people working on the task the same (assignment units).
• When you want to keep the resource working on a task at a certain percentage of his or her available hours.

Here are a few tips about this type of task:

• This type usually isn't used as much as fixed work and fixed duration.
• Fixed unit is Project's default.
• Note! I rarely used fixed units. I mainly use fixed work and fixed duration.

Fixed Work Tasks

Fixed work tasks means that in the formula Duration * Units = Work the work is fixed. Use Fixed Work tasks in situations such as:

• When the effort required is the first thing you estimate.
• When the effort required is the easiest thing to estimate. Estimating effort is usually easier and more accurate than estimating duration.
• When your resources give you task estimates in work hours. For example, developers and engineers typically give work estimates in hours.

Fixed Duration Tasks

Fixed duration tasks means that in the formula Duration * Units = Work the duration is fixed. Use Fixed Duration tasks in situations such as:

• When the duration is the first thing you estimate.
• If the duration stays the same when adding resources, such as training or backing up a computer system.
• Tasks that always have a group of resources assigned, such as meetings or training.
• When the deadline is so tight that it's the primary driver for the duration of the task. You have to make it work within the available timeframe. This situation has been prevalent in most of the organizations I've worked with.
• When the workload isn't your problem, such as when external resources are consultants.

There are two simple guidelines to remember when determining task types. If you remember these guidelines, you'll be able to predict how Microsoft Project will respond as you enter duration, units, and/or work.

Guideline #1: Enter the duration estimate or work estimate and fix that number by setting the Task Type accordingly. Fixing it prevents Project from changing it.

If you enter a Duration estimate, set the Task Type to Fixed Duration.

If you enter a Work estimate, set the Task Type to Fixed Work.

Guideline #2: Provide the second value in the formula Duration * Units = Work and let Project calculate the third value. If you created a fixed duration task, assign the resources you need and let Project calculate the work. If you created a fixed work task, assign the resources and let duration be calculated. If you entered the duration and work, Project only needs to know who will do the task and it will calculate the number of resources needed (units).

Note! Always provide only two of the three values in the formula.

Here's a chart you can print and stick next to your laptop until it becomes second nature to you:

Field that you change	Field calculated if the task is Fixed Duration	Field calculated if the task is Fixed Units	Field calculated if the task is Fixed Work
Work	Units are recalculated	Duration is recalculated	Duration is recalculated
Duration	Work is recalculated	Work is recalculated	Units are recalculated
Units	Work is recalculated	Duration is recalculated	Duration is recalculated

As a general rule the priority of which variable will most likely change is duration, then work, and then units.

If you can master the concept of task types, you'll be well on your way to fully understanding how Project works and how to use its capabilities to your best advantage -- and your frustrations will diminish.

John Reinheimer, PMP, PMI-SP, MCP, has been using Project for 18-plus years. He has worked as a scheduler, project manager, trainer, and PMO developer at several companies, including DirecTV, Mattel, Boeing, Blue Cross Blue Shield of Florida, and Fidelity Information Services. John is an independent consultant currently working with the United States Navy on a $1.7 billion unmanned vehicle program. Contact him at johnnyrein@earthlink.net.