Wednesday, November 19, 2008

Have you ever looked at a burndown, really?

The topic today is about burndown charts. I’d like to make some remarks about what it is used for and why we have it.

First of all, the Burndown Chart is a pretty obvious artifact of Scrum. If you use a wall or whiteboard as your “Scrum Board”, you probably have the burndown close-by and you probably (you should) update it daily. As with most artifacts and mechanisms of Scrum, the basics of the burndown chart is pretty easy to understand. So, at a glance, the burndown chart is self-explanatory.

But is it?

Introduction to Burndown Charts
Let’s start out with discussing what the burndown chart is, mathematically/practically; The burndown is the sum of remaining time for all those items in the sprint backlog, spread out over time along the sprint. So along the X-axis you have your timeline, typically measured in calendar days (at least work-days). Along the Y-axis you have remaining time. You can measure that in Days, in Hours, in Gunships or whatever you want. I recommend that you measure it in (people-)days, though. So, on the daily scrum (the standup meeting) the team goes through all the items in the sprint backlog and they figure out the current remaining time (e.g. by summing up all tasks, or whatever level of detail you have on your scrum board). The sum is plotted in the burndown chart. The result is a plotted line that (hopefully) moves from the top left corner, to the lower right corner. By observing this line the team and everyone else can clearly see how well “on track” the team is: will we reach 0 by the time the sprint is ended?

Can the burndown be "ugly"?
Another important remark (that maybe and unfortunately isn't so obvious) is that the burndown chart is intended as a tool for spotting problems early (by displaying progress daily), which means that it has to be reliable: it has to be the real progress, the hard cold truth - not some made-up half-truthful data that makes the chart "look good". Ever thought of a burndown as "ugly"? I know I have. Sorry, but it is not the burnchart that is ugly (don't kill the messenger): it's the reality. It's the context in which the sprint is executed that is "ugly". As soon as you start "dressing up" the burndown you start hiding the truth. And who will end up biting the dirt for it in the end? Yes, the team...

So, a precondition for having any use what so ever of the burndown chart is that it is as truthful as it is current/up-to-date.

A deeper use of Burndown Charts
But why do you do this at all, track progress and plot it in a burndown? Why display it in this way? Or more specifically: what do you (you, the team, the scrum master, everyone) do with this information?

I know for my own part that I’ve observed hundreds of burndowns by now, and so have all of my colleagues. But I’m not sure that everyone has really spent time reflecting over what the burndown charts mean, other than the immediate, most obvious: that we can see if we have more work remaining than what will be reasonable to finish by the end of the sprint. So, that’s why I wanted to bring this topic up: to get a chance to reflect over how to use the burndown in a deeper, more analytical way: more effectively.

Also, I think most people just reflect over the single, immediate burndown infront of them, without specifically observing or thinking about the burndown in the context of other burndowns from past sprints.

The burndown, in combination with the Scrum Board is an excellent and powerful tool that tells a lot about the immediate climate and environment of the team and the ongoing sprint. If you have knowledge about burndowns and velocity of past sprints, then you have even more powerful information. The burndown – and a set of several burndowns from past sprints – is like a flashlight revealing problems. As soon as there is a problem with progress it is shown in the burndown. But equally important: if you have problems with planning, with product backlog maintenance, with outside disturbance or even with your Scrum implementation as a whole, it will show in those burndowns – if you just know what to look for, and if you realize that this is possible.

So, I guess my advice is: take time and reflect not only over the current burndown, but also reflect over the last 2-3-7-whatever sprints and their burndown, at the same time. I suggest you take a photo of the sprint burndown chart at the end of each sprint and archive it together with records of the estimated and the actual velocity. Then bring that out now and then, let the team get their hands on it and spur discussions about how it looks. Discuss patterns and findings.


Scenarios to reflect over
Below are a couple of made-up burndown charts that I made in Visio (yay!) to visualize some key points. I intended them to represent two consecutive sprints each.


Two sprints showing an interesting tendency...

What would it mean if you see a pattern like above? Here, already from the first few days of each sprint, it is possible to see where the burndown is headed. It is however left like that for too long time, but at least the team acts at some points, by (probably) removing stories from the sprint. So that’s good. But the next sprint shows the same tendency. What if this happens a third time, and a forth? It is clear that the team is over-committing every sprint. I.e. they are not following their actual velocity carefully enough. They are ignoring reality (velocity) and convincing themselves that “next sprint it will be different” – but it never is. So, by observing the burndown over a few sprints you can see that (1) the team acts by removing stories (great), but (2) the team keeps over-committing. It is shown in the burndown as well as in the actual compared to estimated velocity.



Two sprints that show flatlines...

What about the pattern above? Well, the team is unable to complete items – for some reason. It is not resolved (or new problems with the same result keeps appearing) over several sprints. So, the obvious issue here is that the impediment perseveres and renders the team unable to finish items. The not-so-obvious problem here is that nobody seems to act to resolve it. Two sprints is a long time. Remember that Scrum says that impediments should (optimally)be removed in a day. So you really have to issues here that you need to resolve: (1) fix the impediment stopping the team from finishing items, and (2) find out if and why nobody is addressing that impediment.

The two examples above are easy ones, but still I’ve seen them both. I think a lot can be saved by observing both the current burndown and really reflecting over it, but also (not least) by now and then observing the burndown of several sprints in a row.

4 comments:

  1. Nice article! What I do miss is that a burndown does not have to be a sprint burndown. I like product burndowns and project burndowns as well. The reason for this is that sometimes the developers, the team all the rest of us needs to lift our heads and look ahead: to have a larger goal in life. And by creating milestones you can set some kind of project goal and therefore have a project burndown.

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  2. Hi Anna!

    Thanks for the feedback!

    Yes I couldn't agree more. I intentionally focused the article only on the Sprint Burndown, but I was sloppy enough to leave out any comment about other types of useful burndowns.

    I think Project and Product Burndowns (or Release Burndowns which I really like) are excellent means of giving the team a clear sense of direction, of working towards something "bigger" than "only" the immediate next sprint goal.

    BTW, in the Backlog Management Excel tool that I link to in a previous, much older, post I made an early attempt at building such a "Release Burndown" tool too, from the Product Backlog - by measuring StoryPoints sprint by sprint and plotting along a timeline.

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  3. I can also imagine an Impediment Burndown chart to track "change progress". Not sure how useful it would be but it could be a nice artifact to gloat or worry about.

    In addition every Burndown Chart should have it's bigger brother next to it: the "last 8 sprints" velocity diagram with the uncertainity range mapped onto it. Mainly useful for the PO.

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