The Cumulative Flow diagram provides a graphic depiction of how stories are moving through various statuses on the way to being “Done”. It shows us the total scope of a project, grouped by status, and thus lets us know how much of that scope is in a particular status at a given time.

From a cumulative flow diagram, we can see:

• Whether or not value is being delivered as the result of our detail-level activities: Are stories reaching the final status?
• Where the bottlenecks are in our workflow: Is work backing up at a particular status? If so, there is a bottleneck downstream of that status.
• How long it takes something of value to be produced (cycle time): How long does it take to go from entering the initial status to entering the final status?
• Whether the scope of a project is changing: Is the total size of the backlog (the sum of all of the scope, regardless of status) constant, increasing, or decreasing?

Contrasted with a burndown chart, which tells us how much detailed task work (at the iteration level) or project scope (at the project level) is still outstanding at a particular time, the cumulative flow diagram is an indicator of how we’re doing in terms of delivering value. In other words, instead of simply tracking the rate at which we’re completing the backlog, the cumulative flow diagram enables us to measure how efficiently we’re delivering valuable, working product to the customer, and indicates where we need to focus our process improvement efforts.