Statistical Details for Weighted Moving Average Charts
This section describes how control limits are calculated in legacy weighted moving average charts.
Control Limits for UWMA 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
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