Quality Control Charts
Data Visualization

Control charts are used to monitor a process for some quality characteristic such as e.g., thickness, weight, defective fractions, etc.




Shewhart Control Charts for Variables

  • Xbar (R) chart
  • Xbar (S) chart
  • R chart
  • S chart

Shewhart Control Charts for Attributes

  • p chart
  • np chart
  • c chart
  • u chart

Other Control Charts

The following control charts are also used for variables:

  • Levey-Jennings Chart
  • Individual measurements chart
  • Moving range chart

A run sequence plot is a simple line chart that can be used to see a process variation over time, prior to generating a QC chart.

Special Cause Variation

In Aabel, you can optionally apply the Western Electric Company (WECO) rules and the Westgard procedure rules to the appropriate quality control charts.

Western Electric Company (WECO) Rules

The WECO rules can be used for Xbar (R), Xbar (S) and individual measurements charts, and require that groups/subgroups have equal sample sizes.

Westgard Multi-Rules Procedure

The Westgard multi-rules procedure is used to detect trends or shifts by examining individual values to determine the status of the measuring system. Westgard rules are based on sigma and are hence calculated without regard to constant sample sizes. These rules are commonly used with Levey-Jennings chart.

Examples of Aabel QC Charts