I'm struggling to understand what the Average number on the Control Chart is telling me. In this article, which is otherwise very good, the author says "this team takes about 10 days to move an issue from in progress to resolved", and the line on the CC reflects this, but at the top of the CC it says 3d 22h Average. There is no explanation that I can see as to how this average is calculated and how it relates to the line on the chart. The link to the product documentation is also broken.
Can anyone help explain this to me? Thanks in advance.