Gantt charts are a useful tool in the planning phase, to understand the nature of the work to be completed. It clearly shows the tasks to be done, the ordering of the tasks, their start and end dates and who’s doing them. In my experience Gantt Charts showing a medium level of detail are best. If they are too detailed, the Gantt Chart becomes incredibly complex, with hundred of tasks all interconnected in a vast spider’s web of dependencies. Change one thing and it has an unpredictable knock on effect to lots of other parts of the diagram. The management overhead of maintaining it becomes unjustifiable. Too high a level of detail simply doesn’t give the project manager enough information to track and control the work. The only problem with the mid detail approach is that there may not be enough granularity to accurately understand how much work there is yet to do. As we’ll see this is where Burn Down Charts are useful.
The other weakness of the Gantt Chart is it’s inability to show you how it is evolving throughout the project. As you progress, people are continually re-estimating how long they think their tasks will take. The project manager regularly updates the plan. It is impossible to compare the currently estimated time to complete with previous estimates in older versions of the plan. It can be useful to do this, firstly to see how accurate our estimating is, and secondly to check we are not simply “churning”, doing a certain number of hours work each day, only to add even more work to do. One indication of churn on a Gantt chart is the end dating slipping, but this does not necessarily happen, we could be scheduling more tasks simultaneous to tasks already in the plan.
Burn down charts are an idea from the Scrum approach. They do not show the relationship between all the tasks and who’s doing what and when. However they clearly show the amount of work we are currently estimating it will take to complete the project, and how this estimate is changing over time. To put one together is very simple:
Step 1
Everyone estimates how long each of their tasks will take in hours
Step 2
We combine these estimates to come up with an hours remaining to complete figure and plot it on our Burn Down Chart.
Step 3
We regularly update, this figure. Daily is best.
The Chart shows a line, hopefully going down, showing our progress on the project. We can then draw a line from today’s estimate to the zero hours point on the day we want to finish. The slope of this line is called the burn-down velocity. It shows how many hours per day we need to do, to finish on time. Taking account of the current number of resources we can see if this is feasible.
The burn down chart quickly communicates an aggregate figure of where we are in the project. Also it shows how accurate we are at estimating. If we are regularly getting charts that contain up slopes, we know we need to improve our forecasting.
Probably the best approach is to use both charts. The Gantt Chart can be used to create the initial project plan to understand dependencies and the ordering of work and then the Burn Down Chart can track the work throughout the project. I wouldn’t recommend continually trying to reconcile the two – this will be a messy waste of time.
What do you think – how have you used Gantt Charts. Have you ever used Burn Down Charts? As ever interested to hear from you.
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{ 2 comments… read them below or add one }
David,
That was a nice comparison of the two methods on showcase. Where a person would use MS Project to compose a Gantt chart, what tool would be used to create the Burn Down Chart you’ve mentioned? This is the first time I have heard reference to this methodology, but it sounds quite useful.
My 2nd questions is, given your experience with these charts, what should a PM see in terms of a trend for the Burn Down Chart? Will a healthy project display a linearly reducing trend or instead one similar to your example with a faster rate of decay towards the end of the project? I’m curious to know what is expected, so as to form a baseline in using this type of chart the first time through.
Kind regards,
Brad
Hi Brad,
Thanks for your comments. To answer your two questions:
- I have always created burn down charts in Excel – so no special software required
- You would hope that the line is going down in a fairly uniform way. If there is a faster rate of decay at the end it would suggest that everyone is cramming in the work just before the deadline, which could be risky.
David