Cumulative Flow Diagram for Maximum Process Stability (Video)

Although the cumulative flow diagram can be a powerful tool in the hands of every project manager, many fail to recognize the full value of the chart because of the complex explanations that usually go hand in hand with it.

Essentially, the chart offers a concise, coherent visualization of the three metrics of flow – cycle time, throughput, and WIP. In addition, the cumulative flow diagram can synthesize massive amounts of information and present them in a view that anyone can navigate at just a glance. Visualizing your team’s flow this way provides you with both quantitative and qualitative insight into past and existing problems.

The main purpose of the cumulative flow diagram is to show you the stability of your workflow over time and assist you in keeping your team on the right track towards process perfection.

The chart tracks the total number of work items that are in the columns of the In Progress section on your Kanban board each day. It is referred to as cumulative because it accumulates completed tasks over time, as opposed to burning down as the team goes through them. Only include the Backlog in your cumulative flow diagram if the items in it have been committed, and are not just ideas.

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The horizontal axis represents the time frame for which the chart is visualizing data. The vertical axis shows the cumulative number of cards that are In Progress at the various points in time.The differently coloured bands that divide sections of the upward flow are the different stages of your workflow as they appear on the Kanban board itself.

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Similarly to the other modules of premium analytics in Kanbanize, the time frame for which the cumulative flow diagram accounts can be navigated by selecting chunks of time in the supplementary chart below the CFD. With its help, you can zoom in and out of a different period of time and see how stable your team’s workflow was for the given range of days. For example, you can use the navigator to check back on how the stability of the flow was changing on a weekly basis throughout a whole month, quarter or whatever time frame you wish to inspect in more detail.

The predictability of the flow hides “between the lines”.

The top line of a cumulative flow diagram always represents the cumulative arrivals to a process. The bottom line on a CFD always represents the cumulative departures from a process. The vertical difference between those two lines at any reporting interval represents the total Work In Progress in the system. As the author of Actionable Agile Metrics for Predictability Daniel Vacanti explains, “the Cumulative Flow Diagram is all about arrivals and departures”.

If they grow in parallel to each other, the more predictable the flow becomes. If you see that the top and bottom lines of the in progress section of the CFD begin to diverge, this indicates that your work in progress is growing over time, which might be caused by the presence of a bottleneck. This indicates that your cycle time will be growing as well. If those two lines are constantly diverging, your cycle time is constantly increasing.

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Whenever you see plateaus in the departure line of any band of your cumulative flow diagram, they are by definition periods of time with zero throughput in which the work items accumulate cycle time. Depending on which segments you are looking at, flat lines could represent either periods of zero arrivals or periods of zero departures. Usually, you should be more concerned about these flat lines when they represent periods of zero departures because zero departure of work items from the process means nothing is getting done. In other words, no value is being delivered to the customer (or to a downstream step).

The horizontal distance between any two lines of a cumulative flow diagram is a measure of the approximate average cycle time for items that finished between the two arrival and departure lines selected. The most common misconception is that it is a measure of either exact cycle time or exact average cycle time. It is actually a measure of approximate average cycle time. This is due to the fact that the cumulative flow diagram does not show the specific tasks that enter or leave the flow and just accumulates their totals for each process stage. For example, if three tasks entered our flow on March 6th and, on the next day, three tasks departed, the assignments that were completed might be those that entered a day earlier or another three that entered the flow a long time ago. We can’t be absolutely sure about either conclusion just by looking at the diagram. In order to approximately calculate how long it took for items to be completed at a particular reporting interval on average, you need to hover over the point on the bottom line of the CFD that corresponds with the date that you are interested in, and follow the horizontal line backward until it intersects the top line of the CFD in the past.

The slope of any line between any two reporting intervals on a CFD represents the exact average arrival rate of the process state represented by the succeeding band.

The slope of the bottom line is what is technically known as the departure rate of your Kanban board. If the bottom line of your CFD represents the departures from your process, then the slope of that line between any two points (reporting intervals) is your exact average throughput between those two points.

Similarly, if the slope of the bottom line of the CFD is your average throughput, then the slope of the top-most line is your average arrival rate. The slope of that top line represents how fast work is coming into our system, while the slope of the bottom line represents how fast work is leaving our system.

From the perspective of system stability, follow whether your average arrival rate is roughly equal to your average throughput. Use these to calculate whether your cycle time is growing or shrinking over time. The statistics in the cumulative flow diagram are all interrelated.

Beware of disappearing bands on your cumulative flow diagram.

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Sometimes, you may notice that some of the bands on your CFD disappear at certain ranges in time, then return. This might mean that your team frequently decides to skip a certain step in the workflow altogether resulting in that step often not having any work in progress at certain periods that your CFD is visualizing. This may be a hint that there are redundant steps in your flow or that your team fails to understand their value. It would be up to you to decide, given your particular context, whether disappearing bands might indicate inconsistency in how your team interacts with the stages of the workflow.  

The premium cumulative flow diagram comes with specifically designed filters that aim to maximize the value of the chart.

From the left-hand filter, you can set up the time frame that the cumulative flow diagram will visualize. Be sure to include enough days so that you can have at least 10 tasks that were completed during the visualized interval. Otherwise, the system will warn you that there is not enough data for the chart.

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The attribute filter allows you to filter the data visualized on the cumulative flow based on the various card attributes that you have inside your Kanban cards or their position on the board. For example, with its help, you can keep an eye on how the tasks assigned to a particular team member have been flowing through the process over time. Similarly to the other premium analytics, this filter can be set both for this individual chart and globally throughout the module. 

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You can remove any of the stages of your workflow with the help of the specifically designed filters at the top and bottom of the right-hand menu. A typical scenario would be to remove some of the earlier stages of your workflow in order to get a clearer picture of how assignments were progressing from a particular step of your process (e.g. ready for code review) onward.

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The Summary Statistics control provides you with information about the average arrival rate of cards on your Kanban board, average throughput, daily WIP, and average cycle time. The summary will only include data about the stages of your workflow that you have specifically included to visualize.

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With the help of the WIP Tooltips filter, you can modify the information that you see when hovering over parts of the chart. Placing a checkmark on System will give you the total number of items that were in progress on the day over which you hovered.

If you select Stages, the total of work items will be divided for each stage of your workflow. This way, you can see precisely how many cards were placed in any of the columns on your Kanban board at a given point in time.

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The Cycle Time Tooltips filter will help you get an idea of how long it took for tasks to get done. When you place a checkmark on System or Stages, upon hovering over any day of interest, you will see the approximate average cycle time of the tasks that were finished on that day. Similarly to the WIP Tooltips filter, the two filtering options it allows you to choose from will give you a total cycle time for all tasks finished on that day or each work item’s individual cycle time.

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You’ve got two ways of displaying the layers of the cumulative flow diagram. Depending on your preference, they may be smooth or interpolate. 

The cumulative flow diagram is one of the most valuable data visualizations in the Lean world. If you are interested in learning more, don’t hesitate and contact our sales team to request a more in-depth demo of the new Premium CFD powered by ActionableAgile™.

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