ZmR Control Chart in Excel

Use an ZmR Chart to Evaluate the Stability of Short Run Processes

Here is an example of an ZmR Chart created using QI Macros for Excel.

You can use a ZmR Chart to:

  • Short Run SPC (helps you evaluate a short run process)
  • Show multiple characteristics (e.g., hardness, finish, etc.) on one chart
  • Track a part as it goes through the manufacturing process

The ZmR Chart does this by converting the X values into a standardized value, Z, using the average (μ) and standard deviation (σ). There are a number of ways to estimate σ. QI Macros uses standard deviation for each part.

Zi = (Xi- μ)/σ

So the UCL = 3, LCL = -3 and CL = 0

ZmR Chart data usually looks like this:

ZmR chart data example

To create a ZmR Chart, highlight your "Product" data, along with the "Value" of the product. Then, run the macro by selecting the Control Charts (SPC) drop-down menu > Variable (XmR, XbarR/S) > ZmR Chart:

variable control charts

Lastly, your ZmR Chart will be produced:

ZmR Chart Excel using QI Macros

NOTE: If you receive the following prompt, "Invalid Data for ZmR," it is because your data is not sorted:

Invalid Data Prompt from ZmR Chart

To troubleshoot this matter, make sure to sort your short run data using the "Sort" function with Excel.

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