Control limits for the production phase are computed based on the process mean
and standard deviation computed during the OQ stage.
(click to enlarge)
The EWMA control chart is more sensitive to detecting small shifts in the
process mean than the Shewhart control chart and is an alternative to the advanced
control rules. Small drifts in the process mean may indicate a drift in the
calibration of the automated colorimeter that is used to control the amount of
copper in the plating pool.