pert chart

Developing pert Charts.
pert charts contain detailed information relating to the activities necessary to produce the required products. The pert chart should be developed from the product flow diagram by examining the tasks needed to produce the products required. The resources required to complete each product should be identified and the PERT chart should then be updated to reflect these. An alternative style of diagram to the pert chart is the arrow diagram and both of these techniques have their advantages. The main difference is that on the arrow diagram the activity information is shown on the relational link, whereas the pert chart shows activity information within the node, or activity box. The use of either technique should produce the same result. pert charts have become established as the most popular planning technique and have been included in project management software packages.

pert Chart Components.
This course concentrates on the pert chart approach to project planning. PERT charts are made up of a series of activity boxes, each of which depicts a discrete activity or task. Each activity box may contain up to 7 items of information. The top line of the box reflects the earliest point at which the activity could start and finish. The center line should contain descriptive information about the activity and the bottom line should be used to reflect the latest start and finish times. The process of identifying relationships between the activities should only be concerned with logical requirements, in other words it should be assumed that there are no resource constraints when drawing the pert chart. This issue has then to be addressed and appropriate adjustments made. Resolving resource shortfalls and conflicts is the scope of resource planning and scheduling. You may well find it useful to produce sub-diagrams and use these to conduct a brainstorming approach to identifying all possible relationships, prior to building the final network. The project will need to be monitored at various points to ensure that its business and technical integrity is being maintained - the pert chart should also reflect these activities.

Understanding Float.
Reading through the pert chart from left to right gives the total duration of the plan. Reading back through the network, subtracting each duration, shows those activities that have any spare time. This spare time, known as float (shown in red below), is a very useful concept in relation to resource scheduling and smoothing.

Critical Path.
Once the resources required to complete each product have been identified and the pert chart updated to reflect these, then the start and finish dates can be added. With the shape and size of the project now visible, the total cost of the resources for each planning period can be calculated. The PERT chart also clearly identifies the critical path, which is the sequence of related activities which will take the longest time. The critical path is an invaluable concept in project planning - as it defines that sequence of activities that should take the longest time.

Float.
Float is a measure of the amount of time an activity can be delayed without affecting subsequent activities. The amount of float indicates the extent of time that the activity can be delayed without putting back the end date of the overall project (or sub-project). Activities that have an associated float are natural candidates to be delayed when other activities are suffering from problems or overruns. The critical path is defined as the series of activities which have zero float. There will always be a critical path running through a project from the first activity to the last. However, any task, if subjected to sufficient delay; may itself become critical - and this will occur at the point when its float has been entirely consumed by the passage of time. In larger projects, particularly as the project nears completion a number of the arms of the network may contain zero float i.e. the project may contain numerous critical paths. The critical path is an important feature in project planning and control and is usually highlighted on the network in some manner - e.g. bold print, red or a different style of line. It is important to remember that the critical path is not defined at the initial planning stage and then set in stone. As the project progresses and planned activities overrun the network should be frequently updated to ensure that it continues to reflect the true status of the project. The failure to do this is a common reason for projects going out of control and ultimately failing.

Software Packages.
Over the past ten years project management software packages have become increasingly sophisticated and widely used. They can be of great assistance to the staff
involved in managing a project - enabling the more effective tracking of the many interrelated variables and tasks that come into play. Most of these packages will run on a reasonably well specified personal computer and their capabilities vary considerably in depth and sophistication. The features they usually include are:
1. Planning, tracking and monitoring - these most common features provide for planning and tracking of the projects tasks, resources and costs. Usually the software also provides impact assessments of planned deviations and resource and schedule projections.
2. Reports, which may be supported by a full range of Gantt charts, network diagrams, tabular summaries and business graphics.
3. A project calendar which enables the specification of non-working periods such as weekends and holidays. These calendars usually become the basis for all computer assisted resource scheduling.
4. A what-if analysis facility. Some packages can perform a comparative analysis and display the new against the old project plan, enabling easy management review of the options.
5. A multi-project analysis facility. Some of the more sophisticated packages feature a single, comprehensive database enabling cross-project analysis and reporting.

Aggregation, Leveling & Smoothing.
With reference to the tasks, or activities, identified in the plans; the next job is to allocate resources to these tasks. At this stage each task should be dealt with in isolation - it would be premature to attempt to optimize the overall efficiency of matching tasks to the resources allocated. The allocation of resources to tasks should be carried out on a 'best estimate' of how to address the workload requirements. Three techniques can then be applied to ensure the practical and efficient use of resources. Resource aggregation involves compiling a day-by-day total of demand for each type of resource and representing this information in a histogram. The comparison of the daily demand for each resource type against the resource availability profile should highlight any problem areas. For example, a shortfall in the availability of a particular resource type at any point in time.

Critical Path Considerations.
A final point worth noting in the area of resource planning, especially in relation to resource smoothing concerns the critical path. Some planners tend to see the critical path as a sacred sequence of activities that should be left untouched whilst other activities are 'smoothed'. An alternative point of view is that the critical path results from a series of activities which have suffered from a lack of resources being allocated to them and therefore should be seen as the first line of attack. The correct interpretation will vary, depending on the characteristics of each project.

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