Shewhart Control Charts for Variables

S Control Chart

  • Control limits for S control chart are calculated as shown below.

Calculating Control Limits for S Control Chart

Example Graph

S Control Chart Concerning Semiconductor Processing*

Shewhart S Control Chart

* Engineering Statistics Handbook. Process and Product Monitoring and Control. http://www.itl.nist.gov:

  • A case study of a lithography process that included measurements from five sites on each wafer, three wafers in a cassette (of equal sample size) and thirty cassettes of wafers. The quality characteristic of interest is the width of a line ("Raw Line Width").