Critical Path Analysis & PERT Charts
Planning and scheduling more complex projects The benefit of using CPA over Gantt Charts is that Critical Path Analysis formally identifies tasks which must be completed on time for the whole project to be completed on time, and also identifies which tasks can be delayed for a while if resource needs to be reallocated to catch up on missed tasks. The disadvantage of CPA is that the relation of tasks to time is not as immediately obvious as with Gantt Charts. This can make them more difficult to understand for someone who is not familiar with the technique. A further benefit of Critical Path Analysis is that it helps you to identify the minimum length of ...view middle of the document...
The chart is repeated in figure 1 below: Figure 1. Task List: Planning a custom-written computer project NB: The start week shows when resources become available. Whether a task is parallel or sequential depends largely on context. Task Possible Length start week 1 week 1 week 3 week 1 week 1 week 4 5 days 1 day 2 weeks 2 weeks 2 weeks 3 weeks Type Dependent on...
1. High level analysis 2. Selection of hardware platform 3. Installation and commissioning of hardware 4. Detailed analysis of core modules 5. Detailed analysis of supporting utilities 6. Programming of core modules
sequential sequential 1 parallel 2
sequential 1 sequential 4 sequential 4
7. Programming of supporting modules week 4 8. Quality assurance of core modules 9. Quality assurance of supporting modules 10.Core module training 11.Development of accounting reporting 12.Development of management reporting 13.Development of management analysis 14.Detailed training 15.Documentation week 5 week 5 week 7 week 6 week 6 week 6 week 7 week 4
3 weeks 1 week 1 week 1 day 1 week 1 week 2 weeks 1 week 2 weeks
sequential 5 sequential 6 sequential 7 parallel parallel parallel 6 5 5
sequential 5 sequential 1-13 parallel 13
2. Plot the activities as a circle and arrow diagram Critical Path Analyses are presented using circle and arrow diagrams. In these, circles show events within the project, such as the start and finish of tasks. Circles are normally numbered to allow you to identify them. An arrow running between two event circles shows the activity needed to complete that task. A description of the task is written underneath the arrow. The length of the task is shown above it. By convention, all arrows run left to right. An example of a very simple diagram is shown below:
This shows the start event (circle 1), and the completion of the 'High Level Analysis' task (circle 2). The arrow between them shows the activity of carrying out the High Level Analysis. This activity should take 1 week. Where one activity cannot start until another has been completed, we start the arrow for the dependent activity at the completion event circle of the previous activity. An example of this is shown below:
Here the activities of 'Selecting Hardware' and 'Core Module Analysis' cannot be started until 'High Level Analysis' has been completed. This diagram also brings out a number of other important points: • • • Within Critical Path Analysis, we refer to activities by the numbers in the circles at each end. For example, the task 'Core Module Analysis' would be called 'activity 2 to 3'. 'Select Hardware' would be 'activity 2 to 4'. Activities are not drawn to scale. In the diagram above, activities are 1 week long, 2 weeks long, and 1 day long. Arrows in this case are all the same length. In the example above, you can see numbers above the circles. These show the earliest possible time that this stage in the project will be reached. Here units are whole weeks.
A different case...