About Control Chart Rules

DivePort supports three sets of control chart rules:

Basic Shewhart rules determine that a sample is not in control if any point is above the UCL upper control limit or below the LCL lower control limit.

WECO rules determine that a sample is not in control if any of the following conditions are met:

• Any point is above the UCL or below the LCL.

• Two out of three consecutive points are outside the 2-sigma zone on the same side of the center line.

• Four out of five consecutive points are outside the 1-sigma zone on the same side of the center line.

• Eight consecutive points are on the same side of the center line.

Nelson rules determine that a sample is not in control if any of the following conditions are met:

• Any point is above the UCL or below the LCL.

• Nine consecutive points are on the same side of the center line.

• Six consecutive points are continually increasing or decreasing.

• Fourteen consecutive points alternate between increasing and decreasing.

• Two out of three consecutive points are outside the 2-sigma zone on the same side of the center line.

• Four out of five consecutive points are outside the 1-sigma zone on the same side of the center line.

• Fifteen consecutive points are inside the 1-sigma zone.

• Eight consecutive points are outside the 1-sigma zone (on either side of the center line).