A Sprint Burndown chart is a tool which Team can use to measure how close they are to meeting their Sprint Goal. Burndown charts show the trend of work remaining across time in a Sprint, a release, or a product. The source of raw data for a burndown is the Sprint Backlog, with work remaining tracked on the vertical axis and the time period (days of a Sprint) tracked on the horizontal axis. The Sprint Backlog is just the collection of tasks which represent the Team’s current understanding of how they plan to achieve the Sprint Goal.
When a Sprint Backlog item – a single task or deliverable defined and estimated by a Team member – moves from in progress to done, it’s estimate is removed from the total estimated work remaining in the Sprint. There are two way to count the remaining work. One, as a summation of the estimation of all the backlog items committed to be done in a sprint or second, as a summation of task breakdown estimation in hours.
The team can gather enough information from the burndown chart. They can also use it in their retrospectives to look for common patterns and behaviors.
As you can see, in the above example, the chart is flat between Day 3 and Day 5 and again between Day 10 and Day 11. The team can retrospect as to why that happened and what can be done to avoid it. The above burndown chart is of a team whose sprint started on Wednesday and ended on two weeks later on Tuesday. In this case, the flatline is because of weekends(Saturday and Sunday).
This can also tell if any new work is added into the sprint. The trend will show upward when that happens.
Sprint Burndown provide patterns and these patterns provide an opportunity for the Team to discuss what is really going on. If the Team is confident they can still fulfill the Sprint Goal regardless of how the data is displayed in the Sprint Burndown chart, the Product Owner and the ScrumMaster should always respect the judgment of the Team.