06 Sep 2012

Where is my Critical Path?

  • Project Management

So just where is my critical path?

Light Speed: Shown is a cliff top path - example of a path that is critical to follow

CPA is a planning and project management tool that we use here at LSITS to ensure a project is completed as quickly as possible, and resources used as efficiently as possible. It is vital that the information obtained at the start of the project is accurate and therefore we take time out to understand our clients requirements and make sure that everything is captured. 

Light Speed: A list of Activities that have interconnections that are the paths

In the diagram above the duration of each activity is listed above each node. For each path, add the duration of each node to determine its total duration. The critical path is the one with the longest duration.

There are three paths in the example diagram above.

Light Speed: Shown is a list of paths - the longest one is 18 days and is the Critical Path

Identifying the critical path to any project will:

  • Help you identify the activities that must be completed on time in order to complete the whole project on time.
  • Show you which tasks can be delayed and for how long without impacting the overall project schedule.
  • Calculate the minimum amount of time it will take to complete the project.
  • Tell you the earliest and latest dates each activity can start on in order to maintain the schedule. 

Project managers can also apply the critical path methodology technique to determine the amount of float on various logical network paths in the project schedule network to determine the minimum total project duration.

Determining my float..........

Light Speed: shown is a beautiful day with someone floating in a nice calm blue sea

Oh the magical thought of float.

Floating in tropical, warm waters under a bright blue Caribbean sky! 

Ooops.....we are not discussing that type of float. Moreover, back  to reality and project management. Float in project management terms is the amount of time an activity can slip before it causes your project to be delayed. If an activity on the Critical Path gets delayed, the project will get delayed. But, what if other project activities get delayed? How will such delays impact the project schedule? How long can you wait for an activity to complete before it impacts the project completion? Calculate the float!

Float is sometimes referred to as slack and determining your float using the Critical Path Method (CPM) is fairly easy. Once you have established your critical path in your project you will be aware that each activity within the critical path has a float of zero and if any of those activities slip, the project will be delayed.

Light Speed: This is a chart of activities showing that all CP activities have a float of zero - this can be used to determine the Float of th eother activities in a particular path

Light Speed: shows an example of determining the float of an activity is 2 days

If you take the longest path which is not the critical path, which in the example above is 16 days, subtract it's duration from the duration of the critical path you can work out the float for each of the activities on that path, which in this example is 2 days.

You can continue doing the same for each subsequent longest path until each activities float has been determined. If an activity is on two paths, it's float will be based on the longer path that it belongs to.

Using the critical path diagram above activities 2, 3, 4 and 6 are on the critical path so they have a float of zero

The next longest path is activities 1, 3, 4 and 6 and since activities 3, 4 and 6 are on the critical path, their float will remain as zero but the remaining activity, in this case activity 1, will have a float determined by the duration of the critical path minus the duration of this path.

Thus: 18 - 16 = 2. So Activity 1 has a float of 2.

The next longest path also has activity 2 in it which is in the critical path, so it will have a float of 0 and the remaining activity, activity 5 will have the float determined by the duration of the critical path minus the duration of this path.

Thus: 18 - 4 = 14. So Activity 5 has a float of 14.

Therefore, so long as Activity 5 doesn't slip by more than 14 days, it won't cause a delay to the project.

Determining the float of each activity within your project plan enables you to make informed decisions about the amount of extra time you may or may not have for each activity and allows you to manage your project accordingly.

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