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Thursday, September 27, 2007

Activity-On-Node Scheduling

(NOTE: I am using a lot of pictures in this blog post, so it may take a few minutes to fully load.)

I'm going to have to push the next part of my forecasting series back another day. I will be having a quiz on AON scheduling diagrams later today. I thought that doing a quick blog entry on it would be a better idea. It could be informative for my readers, and good review for my class.

Activity-On-Node (AON) is a form of scheduling that is used on large tasks with many parts. With each part, you want to have an idea how long a task will take. Once you have an idea, you can better schedule your resources. Lets look at the diagram.

The nodes represent activities and the arrows connect each activity. Written in each node will be a group of numbers and an activity designator.
ES=Earliest Start
LS=Latest Start
EF=Earliest Finish
LF=Latest Finish
Duration=Expected time to complete task

Let's fill in our designations and task durations.

Now we know what to call each task and how long they should take. The next step is known as the FORWARD PASS. This step take the earliest step time and adds the duration to come up with the earliest finish time. This earliest finish time becomes the earliest start time for the next node. In the event that there are two events that feed into another one, the longest of the early finish times will act as the new early start time. I hope you followed that, but if not, hopefully this diagram will help:

Once you find the earliest finish times on the last node, we need to do a BACKWARDS PASS. Take the earliest finish time from the last node and use the same number in the latest finish time. Then go back, using subtracting to fill in the bottom parts of the nodes.

A little subtraction of finish times minus start times will then help you find your slack for each node.

Finally, see where slack is zero to find your critical path is. Your critical path represents the tasks that will require the most focus to ensure your project is finished in the most efficient amount of time.

I hope this helps. This is a good tool for project managers. If you have any comments, please let me know.
--Sincerely, Trevor Stasik

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