 | The Burndown |
Most stakeholders are viewing progress from 30,000 feet. They are less concerned with how the Dev Team is faring on a given day and what roadblocks might be hindering their pace. The emphasis is on strategizing time and resources. If a project is far ahead or behind schedule, they will want to make strategic decisions to maximize the company’s forward momentum and minimize the risk of overcommitting resources.
The Burndown is the artifact that allows the PO and any stakeholders to see what kind of progress the team is making and estimate whether they will finish all work on time (or ahead or behind schedule).
A burndown chart plots work against time. The Y axis represents Story Points remaining, while the X axis represents linear time, terminating at the end of the sprint. At the beginning of the sprint, the line should be at its highest point on the Y axis. Each day, as stories/tasks are completed, story points are subtracted from the remaining work total, resulting in a drop on the Y axis. If the same number of story points are completed each day, the resulting line will stretch diagonally from the top left to the bottom right of the graph (“Estimated Burndown” shown in the chart above). A “Real Burndown” will usually be be less uniform, but still progress from top left to bottom right.
On any given day, the PO (or others) can tell whether the team is on schedule. If the Real Burndown line (red in the chart) is higher than the Estimated Burndown (blue), then more story points remain than expected, and the team is behind schedule. Conversely, if the red line is below the blue, then the team is ahead of schedule.
Velocity
Velocity is the rate at which a given team completes Story Points each day. Note that velocity only has meaning in comparison with previous work completed by a team and with that same team’s estimate of items in the Product Backlog. After a few sprints are complete, everage velocity estimates tend to stabilize, resulting in the ability to accurately predict how much time will be required to complete all items in the backlog. Since the key stakeholders ultimately care about time and resources (rather than effort, complexity, or story points), velocity finally allows us to deal in a currency they understand.
With velocity established, the PO can assess, and communicate with stakeholders, how long a project will take to complete and whether any adjustments could/should be made to the long-term strategy.