Laney u' Chart | u Prime Charts in Excel

The purpose of a u chart is to determine stability of "counted" data (e.g., errors per bill, dents in a car door, etc.) when there can be more than one defect per unit and the sample size varies.

The u chart works for most data sets. However, if your data meets certain criteria you may need to consider an XmR chart or a Laney u' Chart (u Prime).

Consider an XmR chart if the denominator does not vary widely from sample to sample and your u chart looks like the one below where the control limits seem too narrow for the data and most points are highlighted as unstable.

compare u chart to laney u chart

Here is an XmR Individuals chart run on the same data:

xmr chart compare to laney u chart

Consider a Laney u' Chart (u Prime) if: the sample sizes in your denominator vary greatly.

A Laney u' Chart (u Prime) will have wider control limits than the u chart and it will have varying control limits that may help identify unstable points not identified by the XmR chart. Here is a Laney u' Chart of the same data.

laney u chart

QI Macros add-in for Excel contains a Laney u' Chart template. Click on QI Macros, SPC Charts, u chart to open up the u chart template. Then click on the U' Chart Skyline tab at the bottom to open up the Laney u' Chart (u Prime) template.


Learn More...

Why Choose QI Macros Over Other Control Chart Software?



  • Only $279 USD - less with quantity discounts
  • No annual subscription fees
  • Free technical support

easy to use

Easy to Use

  • Works right in Excel
  • Create a chart in seconds
  • Easy to customize & share charts

proven and trusted

Proven and Trusted

  • More than 100,000 users
  • In More than 80 countries
  • Five Star CNET Rating - Virus free