In "Minding the Gap," I wrote about a gap growing steadily over 3 sprints between the initial release plan and the reality that unfolds over those 3 sprints.  The first picture in that post is shown below.

In the "Minding the Gap" post, it may not have been readily evident how the gap was growing and how it would have been revealed in earlier versions of the release burnup.  In this post, I will show how the gap grows over the 3 sprints as revealed by the release burnup chart.  Here is the release burnup as it would have appeared at the end of sprint 1:

At this point the gap is tiny.  At the current velocity, the release plan falls short by only 5 points at sprint 5, the planned release date.  The barely perceptable gap is revealed most clearly in this chart by the position of the red triangle, representing the Projected Release Date, relative to the blue triangle, representing the Planned Release Date.  This tiny gap is the early warning that things are not going according to plan.  The next picture shows the release burnup at the end of sprint 2:

At the end of sprint 2, a lower velocity shifts the projection of completed points far to the right on the sprint timeline.  The gap has grown to 29 points.  Moving on to sprint 3:

By the end of sprint 3 the gap is greater still.  Despite a higher velocity in sprint 3, an increase in a number of total points planned for the release pushes the project release date even further to the left.  The gap between the release target and the projected number of completed points is now 34 points.  Unless a change is made to the plan or impediments stifling the team's velocity are removed, current reality will trump the plan.