Time-Weighted Control Charts Overview
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With the exception of moving average charts, Minitab's time-weighted control charts are weighted either by previous subgroup means or a target value. The advantage of using time-weighted control charts is the ability to detect small shifts from the target value.

For more information about control charts, see Control Charts Overview.

Choosing a time-weighted control chart

Minitab offers three time-weighted control charts:

·    Moving Average -  a chart of unweighted moving averages

·    EWMA -  a chart of exponentially weighted moving averages

·    CUSUM -  a chart of the cumulative sum of the deviations from a nominal specification

EWMA, Moving Average, and CUSUM produce control charts for either data in subgroups or individual observations. Typically, you use these charts to evaluate the process level. However, you can also use EWMA and CUSUM charts to plot control charts for subgroup ranges or standard deviations to evaluate process variation. See [11] and [25] for a discussion.