When Should You Recalculate Control Limits?

QI Macros Process Change Wizard adjusts limits automatically.

Show Process Changes on Control Charts using
QI Macros:

  1. Click on a Control Chart.
  2. Click on QI Macros Chart menu > Process Change Wizard.
  3. QI Macros find any runs and trends in the data and adjust the chart for you..

Go Deeper: Has a process change occured within your data set?

Based on calls to our tech support line, most folks do not know when they should recalculate control limits on a control chart. The short answer is: when the process changes. But what if you are not sure if your process has changed?

QI Macros Can Help!

  • QI Macros Process Change Wizard will analyze your data and identify potential runs and/or trends.
  • QI Macros built-in rules mistake proof the process change (runs and trends) recognition process.
  • QI Macros wizard automatically recalculates the control limits and reruns stability analysis saving you tons of time.

You will look like an expert and will have extra time to spend investigating what the chart tells you rather than just drawing it.

To use the QI Macros Process Change Wizard

  1. Just select your chart:
  2. control limits before recalculation

  3. Then, choose the "Process Change Wizard" tool from QIMacros Chart > "Control Chart Tools" section:
  4. qi-macros-chart-menu

  5. The Process Change Wizard will analyze your data and change control limit calculations based on where it identifies runs and/or trends in your data. It will also re-run stability analysis with the new limits. These changes to control limit calculations are referred to using various terms including: steps, phases and stages.
  6. example of control limit steps (aka control limit phases or control limit stages) after process change

    Note: Process Change Wizard output based on Rule #4 (n points in a row above or below center line) and Rule #5 (Trends of n points in a row increasing or decreasing) ONLY, and uses the control chart rules currently selected by end user. QI Macros defaults to Montgomery Rules, but these can be changed.

    For XmR, XbarR, and XbarS charts, only use the Process Change Wizard on the X charts - never the R or S charts.

Bimodal Distributions

If your data set has a bimodal distribution (2 centers of data or multiple peaks), QI Macros' Process Change Wizard will make its best guess to provide process change recommendations. However, if you find that the wizard does not recommend ALL instances where you believe a process change should be placed, run a Histogram on your data set:

bimodal distribution histogram example

Does your data set have (2) clear centers of data or multiple peaks? If so, your data set's distribution is bimodal and you may need to input your own, additional process changes.

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