SPCCalculator(xls 6)

Once you have constructed the control charts, you need to interpret each chart's pattern to determine whether the process is "in control" or "out of control."
Below are several common indicators of being out of control, i.e. something has changed in the process being studied. Each Chart is judged separately.

Divide the control chart into equal-size zones (A, B, and C) above and below the center line as shown below. These zones are equal to 1, 2 and 3 standard deviations from the "center line" Then apply the following tests:
"Out of control" conditions occurs if any one of the following situations is found:
1 Any occurrence of a point outside of the either control limits: UCL or LCL
2 Two out of three points in Zone A on the same side of the center line
3 Four out of five points in Zone B or beyond on the same side of the center line
4 Nine consecutive points on the same side of the center line
5 Six consecutive points increasing or decreasing
6 Fourteen consecutive points alternating up and down
7 Fifteen consecutive points in either Zone C (above or below the center line)

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