Biggy Zahn

Biggy Zahn

What is Work, Duration and Assignment Units?

Formula: Duration = Work / assignment Units

This is the golden MS Project formula. When working with resources, it is essential to understand how MS Project calculates.

Formula: Duration = Work / assignment Units

For instance: 5 days = 40 hours / 100%

Duration is the length of working time between the start and finish of a task. MS Project bases the calculation of a task’s duration on the amount of work and the amount of resource units assigned to it.

Let’s practice

For instance, 80 hours of work done by two people means the task will take 5 days duration (assuming 8hr work days). The working time for a task is defined by the project calendar, resource calendar, task calendar, or any custom calendars you set for a project.


Work is the amount of effort, measured in time units (like hours or days), that a resource needs to complete the task. The total work for a task is the sum of all those time units, no matter how many resources are assigned to the task. Think of work as the amount of hours you would be charged for if the resource were an external consultant. This includes toilet breaks, an incidental personal email and daydreaming (gross amount of hours) and does not regard how the hours are spread over the duration of the task. Also note that if you got your work estimates from an internal party, such as a systems architect, you might have received a net estimate of hours (without all the things that make us human).

Resource Units

Resource Units indicate how much of a resource’s available time, according to the resource calendar, is being used to work on a particular task. Resources are the people, equipment, or other materials that are applied to completing a task. On a task in the project schedule, resource effort is expressed as units. You can consider units here as the average speed of the task.

If you have 100 miles to cover (work), and your average speed is higher (units), you will be there faster (duration). If you have 100 hours of paint work to do, and your average speed is 2 painters, you will be ready faster than with an average speed of 1 painter.

What is Work, Duration and Assignment Units?1

Take care!

Do not mistake resource units for resource availability to the project. Resource availability is a resource feature. ‘Units’ is a task feature.

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How to reschedule all incomplete work with one button?

When you are at a point where you have updated the actual progress on tasks and re-examined the ETC (estimate to complete) for these tasks (i.e. remaining duration), some tasks may not have been finished as planned.

Reschedule incomplete work

In other words, only part of the task has been done, and there is still some work to do. Possible reasons are that someone was ill last week, or someone needed to solve a critical incident in another project, that supplies were not delivered yet, etc. Since these activities still need to be done, you need to reschedule this uncompleted part of the task to a time in the future, preferably as soon as possible, to reduce the (potential) total delay.

Only one button

Microsoft Project has a button that does this all at once: Project tab > Update Project > Reschedule uncompleted work to start after: <select a date>

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Adding a dependency by typing the linking path

Adding a dependency – one option

Creating links between schedules can be done in several ways. One way is by simply typing the link path in the predecessor column. Please make sure you refer to the correct line number in the other schedule (e.g. <name of other schedule\3).

Adding a dependency by typing the linking path1

If you are working on a Project Server you will see the name of the file, if you are working on a stand-alone version of MS Project you will also see your file’s location on your computer.

At opening, the other schedule will see the ‘Link Between Projects’ window with the possibility to ‘accept’ the creation of the external link (click on the second line ‘Delivery Parts B’ in the Link Between Projects window > Accept > Close). When this edit to this schedule is saved, then the link is finalized.

Adding a dependency by typing the linking path2


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Check on dangling tasks

When your schedule is ready to perform a Critical Path Analysis, you must check if the network of activities is a nice closed network (all tasks have a predecessor and successor except for the start and finish milestones) and you should do a check on any dangling tasks.

What is a dangling task?

A dangling task, or a ‘dangler‘ is a task or milestone that is not connected on both sides and as such will not be recalculated when other tasks in the schedule move. If you have a dangler it is hard to trust your schedule and you need to take more manual actions to have your schedule up-to-date.

Check on dangling tasks1

In the template that is delivered to everybody as part of our e-course, we have create a custom filter that shows all tasks for which there is either no predecessor set, no successor set or neither are set. You could create this filter yourself of course by going to more filters in the filters menu.

Tip: use it as a highlight filter to include the context of the danglers.

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Dependencies with other projects in MS Project

Your project will likely have deliveries or other dependencies with other projects in MS Project. These dependencies can also be modeled with MS Project and will look exactly the same as links within projects: it is a black arrow going from one task to the other.

Big difference however, is that now the link starts from a task or milestone in one schedule and ends at a task or milestone in the other schedule.

For instance in Project ABC the task ‘Assembly parts’ has a dependency with task ‘Delivery parts for assembly’ in Project DEF. (the assembly can start after the delivery took place)

Project ABC

Dependencies with other projects in MS Project1


Project DEF

Dependencies with other projects in MS Project2

In the printscreen below the task ‘Delivery parts for assembly’ is a task from another project:

Dependencies with other projects in MS Project3

Link between projects

A ‘link between projects’ is a predecessor/successor relationship, just like a normal task relationship. The idea is that the link introduces a knock-on effect with regard to changes in timing; when the date of the predecessor in the first schedule shifts, the successor in the next schedule will shift accordingly.

By default, MS Project will show an acceptance window in the second schedule first, so that you are aware of how your schedule will change, before it is being changed. This window will be explained in a later topic.

Learn it the best way from the experts

You can create a ‘link between projects’ by having both schedules in one temporary file or master file and link them up in here. This concept we fully explain in our e-course Critical Path Management.

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The S-curves in MS Project

There is always a lot to do about S-curves in MS Project. It is a greatly appreciated tool for managers to assess your projects status quickly.

The s-curves in MS Project1

An S-curve is defined as:

“A display of cumulative costs, labor hours or other quantities plotted against time. The name derives from the S-like shape of the curve, flatter at the beginning and end and steeper in the middle, which is typical of most projects. The beginning represents a slow, deliberate but accelerating start, while the end represents a deceleration as the work runs out.”

Source: Wideman Comparative Glossary of Common Project Management Terms v2.1 Copyright R. Max Wideman, May 2001

Before the 2013/2016 version of MS Project, it was not possible to get S-curves directly from the tool as it dit not supply cumulative values and as such was not capable of drawing these lines that build on information of earlier weeks. The 2013/2016 version is capable of doing that using the Reports tab of MS Project.

There are a variety of S-curves that are applicable to project management applications, including:

  • Hours versus Time – Interesting for labor-intensive projects, whereas man hours earn the project’s value.
  • Costs versus Time – If the project’s cost breakdown also contains a significant portion of non-labor components (materials).

S-curves can either show absolute values or relative values. Absolute would be expressed as 500 of the 1000 hours still to go, whereas relative values would be expressed as 50% of the work still to go, or 50% of the costs still to incur.

Usually S-curves would show three lines (curves)

  1. The baseline curve – how the work or costs would evolve according to the baseline
  2. The target (forecast) curve – how the work or costs are now scheduled to evolve
  3. The actuals curve – how the work or costs actually have evolved. Obviously, as the project is still progressing this curve is cut-off on a certain date. This is of course the status date

How is the S-curve report actually used?

Consider the following scenario’s:

  • The target (forecast) curve (your current schedule) compared to your baseline shows you more work than expected, this means you have to put in extra people to make up for delays caused by issues, holidays, sickness, etc.
  • The target (forecast) curve (your current schedule) compared to your baseline ends further to the right, this means that your project will be delayed if you do not take action.
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Why is it important to focus on the critical path?

As the critical path determines the finish date of the project, this is where the main focus for the project manager/planner should be. For instance, the critical path should be free from any (unrealistic) resource overallocation. If these tasks can only be performed by one resource, the actual critical path will be longer as this limited resource problem does affect the end date as well.

Managing the critical path

This can be done in several ways, among which:

  • Work overtime
  • Reassign to other resources with more availability
  • Align on the specs before you start, to avoid rework
  • Fast Tracking: Have tasks run in parallel to shorten the total duration
  • Crashing: Add resources to tasks on the critical path so the duration of these tasks decreases
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How to create constraints

Constraints are created when:

  • Dates are typed into the start or finish columns or
  • If you double click on a task and change the constraint type in the Advanced tab of the task information window.How to create constraints1

If a task has a constraint date attached to it you will immediately see a small calendar in the indicator column. If you hover with your mouse over it, it will tell you the constraint type and date.

Types of constraints

Listed below are the types of constraints that exist in MS Project:

How to create constraints2


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