6.2 Gantt chart
Gantt charts show all the key stages of a project and their duration as a bar chart, with the time-scale across the top. The key stages are placed on the bar chart in sequence, starting in the top left-hand corner and ending in the bottom right-hand corner (Figure 7 – Gantt chart for directory production). A Gantt chart can be drawn quickly and easily and is often the first tool a project manager uses to provide a rough estimate of the time that it will take to complete the key tasks. Sometimes it is useful to start with the target deadline for completion of the whole project, because it is soon apparent if the timescale is too short or unnecessarily long. The detailed Gantt chart is usually constructed after the main objectives have been determined.
In this example, key stage K (‘organise distribution’) starts at week 23 so that its end-point coincides with key stage L (‘distribute directory’). However, K could begin as early as week 17, as soon as key stage J is completed. Key stage K is therefore said to have slack. Key stage H (‘agree print contract’), has been placed to end at week 12. However, it could end as late as week 22, because key stage I (‘print directory’), does not begin until week 23. Key stage H is therefore said to have float. Float time can be indicated on the chart by adding a line ahead of the bar to the latest possible end-point. Slack and float show you where there is flexibility in the schedule, and this can be useful when you need to gain time once the project is up and running.
You can add other information to a Gantt chart, for example:
milestones – if you have special checkpoints, you can show them by using a symbol such as a diamond or triangle;
project meetings could be indicated by another symbol such as a circle;
reviews of progress could be indicated by a square.
For a complex project you may decide to produce a separate Gantt chart for each of the key stages. If you do this shortly before each key stage begins, you will be able to take any last-minute eventualities into account. These charts provide a useful tool for monitoring and control as the project progresses.
Imagine that managers in your organisation are considering developing a directory to be given to new staff appointed, as part of the induction process. You expect that you will be asked to manage this project. You want to be well prepared for the meeting at which the potential project will be discussed.
Draw up a list of the tasks involved in the project and organise them into key stages on a logic diagram. Now turn this into a Gantt chart to show how long it will take to produce the directory. Use your own judgement to estimate how long each stage would take.
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Click here to access a blank Gantt chart
The amount of time you allowed for this project depends on how you applied your knowledge of your own organisation. This should have led you to allow time for each of the tasks that form sequences that must be completed before a subsequent task can start (for example, you should have completed planning the data collection before you collected the data and you should have done most of this before you started writing up the text). You might have allowed some overlap of these activities if some progress was possible before the previous activity was complete; for example, you might have anticipated that some of the text could be produced before the data collection had been completed.
If your Gantt chart demonstrated that the whole job could be completed in fewer than the 28 weeks that were needed in our example, the Gantt chart for directory production, compare your chart with it to see where the differences occurred and consider how realistic your estimate is. It might, of course, be possible to complete the project more quickly in your organisation, particularly if there is agreement to invest additional resources to speed up some of the activities. Remember, however, that if consultation and agreement are required, time must be allowed to arrange meetings with key stakeholders. Similarly, you might have estimated that the project would take longer in your organisation because of the way in which your systems work.
Gantt charts are relatively easy to draw by hand, but this doesn't offer the same level of flexibility during monitoring that you would get from a software package. Various programmes are available to assist project managers in scheduling and control. Once the data have been entered, a programme helps you to work on ‘what if’ scenarios, showing what might happen if a key stage is delayed or speeded up. This is more difficult if you are working manually.