Is this post about doing stage shifts?
Sometimes stages are due to a process change, and sometimes stages are due to a jump in the measured value - we need to be able to do both.
There are two parts to your question:
1) Building out control charts.
2) Adding a discrete dimension to Columns (such as the month in your picture) that would partition the calculations.
Here are two posts on how to build control charts in Tableau:
User Defined Functions and Process Control Charts <http://drawingwithnumbers.artisart.org/user-defined-functions-and-process-control-charts/> - I wrote this post based on my work building control charts in Tableau for Southern Maine Health Care, this expands on the “write your own calcs” part of the prior posts and includes a number of tests for in control/out of control signals.