The Label Burndown Chart is a graphical representation of remaining unfinished work (Stories) with that Label. In a Label, the Burndown Chart is located in the Reports tab.
The Burndown Chart is displayed in either Story Count or Points. Configure this setting in Settings > Estimate Scale.
The Burndown Chart displays the unfinished Story Count or Points on a given day.
The start date of the Burndown Chart is the first date that a Story with that Label was completed.
The end date of the Burndown Chart is the most recent date that a Story with that Label was completed.
Actual Stories/Points Remaining is represented by the bold blue line and references the previous day's points/stories remaining, plus points/stories added, minus points/stories removed, minus the number of points in stories completed.
The ideal number of Stories or Points remaining is represented by a diagonal, grey straight-dotted line, starting from the actual stories remaining on the first day of the Label, and falling to 0 on the last day of the Label.
Stories/Points Added is represented by the purple bar and references when points in a story are adjusted up, or when a story with points is added to the Label.
Stories/Points Removed is represented by the yellow bar and references when points in a story are adjusted down or when a story with points is removed from the Label.
Stories/Points Completed is represented by the light green bar and references that day's number of stories or points completed.
The colors on the graph showcase activity in the burndown. The easiest way to understand the graph is to notice the colors with which the bold blue line (Actual Stories/Points Remaining) is affected. For example:
In the image above, we see that the green bar seems to sit on top of the blue line in the chart. The green bar represents stories/points completed; this is designed to represent that the stories completed on that day have pushed down the blue line to where it is currently at. Conversely, the purple bar, which represents points added, is meant to show the addition of points or stories that have contributed to the blue line being pushed up to where it is currently at.