p Chart and u Chart Formats

p and u chart Control Limit Options in QI Macros

p charts and u charts can have upper control limits (UCL) and lower control limits (LCL) that vary with the sample size. QI Macros provides users with options about how these control limits are calculated and displayed.

Flat or skyline limits without 1 and 2 sigma lines (default)

When you run a p chart or u chart in QI Macros, the default format is "flat or skyline limits" that display the UCL, CL, LCL and your data.

How to Choose Between Flat (Skyline) and Wavy Limits

To change the QI Macros default from flat/skyline limits to wavy limits:

1. Click on Control Charts, then Control Chart Rules, then p/u UCL_LCL format.
2. A window will open showing the new format you are selecting. Click OK to change the format.
3. Now run the p chart or u chart again and the control limits will be wavy vs flat/skyline.

Use the QI Macros chart menu to change just one chart.

Here is a p chart with wavy control limits:

p Chart UCL Limited to 100% Since it is a Fraction Defective Chart

Since the p chart is a fraction defective chart, the UCL is limited to 100% and the LCL is limited to 0%

p Chart Calculations for Small Sample Sizes

In certain cases, the standard formulas for control limits on the p chart cannot be used. This condition exists when:

n × pbar < 5

QI Macros p chart template contains a tab for these instances:

Why Choose QI Macros Over Other Control Chart Software?