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Moving Average & Moving Range
Control Chart
The Moving Average and Moving Range charts provide a graph of the moving
average of a process characteristic and the moving range extent. The moving
average is computed as the average of a sample of successive measurement
points. The number of points averaged equals the subgroup size. A new average
is computed for each successive point by throwing away the oldest point and
including the next in sequence. Think of a sliding cell whose width is equal to
the subgroup size moving across the data in sequence order, point by point. At
each new point a new moving average is computed and plotted. The Moving Average
chart gives a picture of how well a process is centered and if it is stable.
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