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Control charts and capability, explained

Short guides with worked examples. Every number on these pages is calculated by the same code the LimitLine app runs and checked against the published source when the site is built.

• How to calculate Cp and Cpk

  Formulas, a worked example checked against NIST, Cpk vs Ppk, and what counts as a good Cpk.

• The I-MR chart (individuals and moving range)

  Build an individuals and moving range chart by hand, with NIST's flow-rate example.

• The 8 Nelson rules for control charts

  All eight tests for special causes: what each pattern looks like and what usually causes it.

• Which control chart should I use?

  Two questions pick the chart: I-MR, X̄-R, X̄-S, p, np, c or u.

• The X̄-R chart (X-bar and range)

  Subgroup means and ranges, the A2/D3/D4 constants, and a worked example with 8 subgroups of 5.

• The p chart (fraction defective)

  Fraction defective with limits per sample size, worked through on NIST's 30 wafers.

• Gauge R&R: is your measurement system good enough?

  How to read % contribution, % study variation and ndc, using the AIAG example.

• How to calculate OEE

  Availability × performance × quality, step by step on one shift, and which loss to attack first.