Content:
1. Introduction to the Cumulative Flow Diagram
2. What's this diagram telling us?
You can find more information about the Analytics module in the dedicated article.
1. Introduction to the Cumulative Flow Diagram:
The Cumulative Flow Diagram aims to show the stability of your process over time. It tracks and accumulates each task that has ever entered or progressed to any stage of your workflow.
Using the diagram, you can get an idea of how your work in progress, throughput, and cycle time change over time.
- The "X" axis represents a timeline
- The "Y" axis is the actual number of the work items. This could be tasks, projects, or anything that you measure on the selected workflow.
Important:
The Cumulative Flow Diagram allows for cycle time recalculation based on working days.
Note: that the X-axis would still display all calendar days/weeks but the average cycle time for the period will be recalculated - this can be seen by hovering the mouse over the graph data.
For example, if a card was started on Friday and finished on Monday, the setting would read 4 days by default (as it would take Saturday and Sunday into consideration).
With the working days option enabled, the tooltip (when hovering with the mouse) would read a cycle time of 1 day for that card, as time spent in the stages would be recalculated to exclude the weekend.
In case that you need precise cycle and log times for internal reporting, use the Advanced search capabilities with the different charts views and widgets.
2. What's this diagram telling us?
The cumulative flow diagram shows the accumulation of work overtime. Every stage of the workflow is represented by a differently colored band. Whenever you complete a task, the number of cards in your "Done" stage rises permanently.
In the example below, you may see that the respective workflow has accumulated more than 500 work items since the selected date.
Note: If you ever see a band going down, then the chart is incorrect since tasks should never disappear.
In general, you can spot whether your process is stable with a single glance by looking at how the top and the bottom line of each band in your cumulative flow diagram are progressing.
Approximate Average Cycle Time:
The horizontal distance between your first and last stage shows the approximate average cycle time for your tasks meaning the time it took you to progress a task from being Requested to Done. When all the bands are progressing in parallel, this means that your process is smooth and the cycle time is consistent.
TIP: Go to Layout in the Controls for this chart and checkmark "Show data control".
This option allows you to zoom in and out of a specific interval within the selected time frame, so you can get a better overview of the band's width.
Note: you can fine-tune your selection by also scrolling vertically.
Work In Progress:
The diagram visualizes the number of work items that are in progress at each stage of your flow.
This can be measured using the vertical distance between the lines of each band. 
If any of the bands start to expand, it means that the stage holds more work items that it can handle i.e tasks are arriving faster than can be processed. This immediately increases cycle time and you need to take some action. In this case, we recommend you establish Work in Progress (WIP) limits.
The WIP limit improves your throughput and reduces the number of unfinished tasks. The team members pull work as they finish what they started.
Average Throughput
Having bands that are progressing in parallel also means that your average throughput is stable and new tasks are entering your workflow in parallel to those that are leaving it. This is the ideal outcome and shows that you can focus your efforts on shortening the cycle times of your assignments.
The bottom blue line of your diagram visualizes the number of deliverables within a certain date.
The slope of that line between any two points shows the average throughput.
The metric is average because not all of the tasks that have entered the stage necessarily leave it at the predetermined time frame. They might be moved to the next stage later in time.
Summary Statistics
You can access the Summary statistics at the top of the Controls for this chart. 
- Summary Statistics:
All values in this table are calculated averages. Each stage in workflow is represented as a row in the Table. Note: The table provides reliable results only when the Kanban system is stable and there is a continuous flow. If there are too many days when 0 items enter the flow or if there is no movement of items in the established process, bias might occur.
Arrival Rate (items/day) - the average number of items per day that enter the flow.
Throughput (items/day) - the average number of items per day that are passing through the system.
Cycle Time (days) - the average number of days that items spend in the stage.
Daily WIP (items) - The average number of "work in progress" items in the stable system
The top row named "SYSTEM" provides overall results for your process, where:
Arrival Rate (items/day) gets the maximum value for the columns.
Throughput (items/day) gets the minimum value for the columns. (this is the average number of items per day that are passing through the system)
Cycle Time (days) - sums up the cycle time for all columns.
Daily WIP (items) - The average number of "work in progress" items in the stable system.