Capability Plot in Excel

One of Six Charts Created Using QI Macros Capability Suite

Create the Same Charts in Minitab's Capability Sixpack™ for a Fraction of the Cost

The Capability Plot is one of six charts created by QI Macros Capability Suite.

The capability plot is just another way to visualize the capability of a process. Below is an explanation of what the 3 lines represent.

Specification: The end points of the specification line are the Upper and Lower Spec Limits.
Within: Standard Deviation looks at the Standard Deviation of SUBGROUPS - (Rbar/d2 or Sbar/c4).
Overall: Standard Deviation looks at the Standard Deviation of ALL DATA.

Compare the Specification Line to either of the other two

If the Within or Overall lines are wider than the spec line, that means you have data points falling outside of the Spec Limits and therefore your process is NOT capable.


capability plot

Not Capable


Compare the Within and Overall lines to each other

The two lines should be about the same if the process is stable. Big differences mean an unstable process.

Capable and Stable


Capable, but NOT Stable


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