Explanation
According to the Project Management Professional (PMP) Reference Materials, a cumulative flow diagram (CFD) is a graphical tool that can help the project manager assess the state of the project by tracking features that are in progress, completed, or scheduled to be worked on. A CFD shows the number of work items in each stage of the workflow over time, and the total amount of work in the system. A CFD can help the project manager identify bottlenecks, delays, scope changes, and variations in the work process. A CFD can also help the project manager monitor the project progress, quality, and delivery rate. A CFD is especially useful for projects that use agile or iterative methods, as it can show the value delivered to the customer on an incremental basis. References: Project Management Professional (PMP) Exam Content Outline, A Guide to the Project Management Body of Knowledge (PMBOK Guide) - Seventh Edition, Cumulative Flow Diagrams.