CFD Charts In Two Minutes

In my Flow Metrics In Five Minutes post I didn’t discuss the CFD chart and said I would do that in a future post. Here is the future post :).

CFD charts are all about understanding work arrivals and work departures to and from the process as well as arrivals and departures to and from different states within the process. The CFD packs a ton of information into a single view. There are four primary metrics visualized in the CFD:

• WIP
• Approximate Average Cycle/Lead Time
• Average Arrival(Start) Rate
• Average Departure(Completion) Rate or Throughput

WIP for any given date is represented by the distance between the top line and the top of the last layer.

Average Arrival Rate for a given period of time is represented by the slope of the top line of the first layer between the starting and ending dates of that time period.

Average Departure Rate for a given period of time is represented by the slope of the top line of the last layer between the starting and ending dates of that time period.

Approximate Average Cycle Time is a horizontal line from the top line to the top of the last layer. It is the approximate average rather than the average because we don’t know specifically what items are completing during that period.

What you ideally want to see with your CFD is consistency. You want your lines for each status to be relatively steady in terms of its slope and the distance between the next line. Consistent distance between the lines means our WIP is remaining consistent. Consistent slopes mean we have consistent rates of arrival and departure. When you start seeing things like jagged lines or large bubbles in certain statuses it is an indication you have instability in your process. By visualizing the flow it becomes very easy to see where you have bottlenecks that you should investigate to determine root cause.

A key misconception of CFDs is that they are a tool for primarily for use with Kanban. CFDs can not only be used for any Lean or Agile process, but for any process period where you want to understand the dynamics of the process flow. In the above example the x-axis is in weeks and the y-axis is the issue count. Note that the CFD chart should only represent issues that have been completed and thus is a historical representation of the work not a real-time representation.

There you have it. CFDs explained in two minutes! Not terribly complex at all.