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| Pert Charts - Free Online Tutorial |
| The information in this free Pert Charts tutorial is taken from "GetAhead in Project Management". GetAhead in project management distils a 4-day class-based course into a highly focused self-study course. Delivered direct to you, each course installs in under one minute and provides you with unlimited training for a lifetime - it's like having your very own project management training library. |
| The Project Management self-development program is available in the following formats... |
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| eBook 3 Multimedia CD-Roms eBook & 3 Multimedia CD-Roms |
Free Pert Charts Tutorial |
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Introduction
Symbols Used |
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In this example, activity A
must be completed before activity C can begin as indicated by the line
that joins the two activity boxes. Activity A requires 5 days and Activity C requires 4 days. This part of the project will therefore last 9 days. The earliest start time for activities right at the beginning of the network are set to zero. The earliest finish time for whichever input activity is the latest is used to establish the earliest start time for the dependent activity. In this example activity A is scheduled to be completed on day 5. Only then can activity C begin. A Simple Example In many cases an activity will be dependent on the completion of more than one preceding activity. In the example shown the two activities A and B must both be completed before activity C can begin. A requires 5 days, B requires 4 days and C requires 4 days. |
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Activities A and B can be carried out in parallel as they are not
dependent upon each other. In this example this part of the project will
also last 9 days. Determining the relationships between activities can be a complicated process and may require a substantial amount of discussion involving numerous personnel across the various departments that may be concerned. 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. Diagrammers may 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. PERT charts, contain detailed information relating to the activities necessary to produce the required products. It should be developed with reference to the product flow diagram. |
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| The top line of the activity box reflects the earliest time at which the activity could start and finish. The centre line should contain descriptive information about the activity and the bottom line should be used to reflect the latest start and finish times. The lines that join activity boxes are used to represent dependency between the activities. | |
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Identifying
Spare Time 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, is a very useful concept in relation to resource scheduling and smoothing. |
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In the example shown activity R is dependent upon the completion of both
of the activities P and Q. However activity P is scheduled to take 5 days
whilst Q should be completed in 2 days. The area of work represented by this part of the network should last 12 days. Activity Q has a float of 3 days - so activity Q could start up to 3 days late or take an extra 3 days to complete without delaying the start of the subsequent activity (R). Reading back through the PERT chart, subtracting each duration, shows those activities that have any spare time. This spare time, known as float, identifies parcels of time that can be used to introduce flexibility into the production sequence. All planning should be iterative, and the drawing of the PERT chart may highlight further products which need to be added to the work breakdown structure and the product flow diagram. The 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. |
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| The PERT chart also clearly identifies the critical path (shown in red above), 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. | |
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Total
& Free Float The above network represents a small project. The activities that are on the critical path (shown in red) have no float, whilst those that lie off the critical path can have an associated float. |
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| In addition to the float associated with a specific activity, two other types of float need to be considered. | |
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| Total Float (shown in yellow above) is shared with all of the other activities in the arm. Therefore using the float in one activity will reduce the float available for the other activities. For example, in the arm PQ the total float is 19. This is because the dependent activity L has a latest start of 23 and the total duration of the PQ arm is 4. That is 23 minus 4 equals 19. | |
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Free Float (shown in yellow above) is the amount of float that the
activity can use up without affecting the earliest start of any other
activity. Only activities that precede a junction can have free float. For
example, the earliest finish of activity Q is 4. The earliest start of the
dependent activity L is 12. Therefore the completion of activity Q could
be delayed for a maximum of 8 without affecting the earliest start of
activity L. 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. Activities that have an associated float are natural candidates to be delayed when other activities are suffering from problems or overruns. |
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The critical path (shown in red) 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. Back to Pert Charts |
| Pert Charts - Free Online Tutorial |
| The information in this free Pertt Charts tutorial is taken from "GetAhead in Project Management". GetAhead in project management distils a 4-day class-based course into a highly focused self-study course. Delivered direct to you, each course installs in under one minute and provides you with unlimited training for a lifetime - it's like having your very own project management training library. |
| The Project Management self-development program is available in the following formats... |
|
|
| eBook 3 Multimedia CD-Roms eBook & 3 Multimedia CD-Roms |
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