Publication date: 09/27/2021

This section describes how control limits are calculated in legacy weighted moving average charts.

Control limits for UWMA charts are computed for each subgroup i as follows:

LCLi =

UCLi =

where:

w is the span parameter (number of terms in moving average)

ni is the sample size of the ith subgroup

k is the number of standard deviations

is the weighted average of the subgroup means

is the estimated process standard deviation

Control limits for EWMA charts are computed as follows:

LCL =

UCL =

where:

r is the EWMA weight parameter (0 < r ≤ 1)

xij is the jth measurement in the ith subgroup, with j = 1, 2, 3,..., ni

ni is the sample size of the ith subgroup

k is the number of standard deviations

is the weighted average of the subgroup means

is the estimated process standard deviation

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