Stair Step Control Limits on a Control Chart
Use Stair Step Limits to Show a Process Change on Control Charts
It's easy to show process changes on a control chart created by QI Macros. The process is different depending on how you create your control chart:
- New Charts Created with a Macro
- Existing Charts Created with a Macro
- Control Chart Templates
- Excel 2007 Workaround for Showing Process Change on Embedded Charts
To calculate two or more sets of control limits on new charts simply leave a blank row between the data points where you want the limits to change:
Select the data including the blank row(s) and run the chart. You should get a chart with two or more sets of control limits:
- Go to the chart and click on the first data point where the process change occurred.
Tip: The first time you click on a point, Excel will select the whole line. Click on the point a second time to select just the point. If you have done this correctly, Excel will highlight your point.
- Click on QI Macros chart menu and select Show Process Change:
- The macros will calculate a new set of control limits starting at the data point you selected. Note: you can do this more than once on a chart. The example below shows three separate sets of control limits:
Don't forget to rerun stability analysis using the new control limits. Click on the chart sheet. Use QI Macros menu to select "Analyze Stability With Control Chart Rules." QI Macros will rerun stability analysis using the new control limits.
- Note: Performing these steps on an X chart will not update the R chart. You will need to update the R chart separately.
Want to Create an Interrupted Time Series Using QI Macros? See Instructions Below:
You can create an Interrupted Time Series chart by simply performing a Show Process Change at the end and beginning of your two different series!
To do so, place a blank row in between your two data sets, and create your Control Chart:
Why Choose QI Macros Over Other Control Chart Software?
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