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Quality and Process Methods > Control Chart Builder > Statistical Details for Control Chart Builder > Statistical Details for U, C, and Laney U′ Charts
Publication date: 05/05/2023

Statistical Details for U, C, and Laney U′ Charts

In Control Chart Builder, the lower and upper control limits, LCL, and UCL, are computed using the following formulas:

U chart LCL = Equation shown here

U chart UCL = Equation shown here

C chart LCL = Equation shown here

C chart UCL = Equation shown here

Laney U′ chart LCL = Equation shown here

Laney U′ chart UCL = Equation shown here

The limits vary with ni.

ui is the number of nonconformities per unit in the ith subgroup. In general, ui = ci/ni.

K is the sigma multiplier and is set to 3 by default

σz is a moving range sigma calculated from the standardized values

ci is the total number of nonconformities in the ith subgroup

ni is the number of inspection units in the ith subgroup

Equation shown here is the average number of nonconformities per unit taken across subgroups. The quantity Equation shown here is computed as a weighted average

Equation shown here

N is the number of subgroups

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