- 1). Distribute your data to revolve around a mean (average). Ensure your measurements are independent of each other. Create a subgroup for each data point and measurement number.
- 2). Add all your measurements in the subgroup and divide by your number of measurements. Calculate the mean of all the means; this will determine your over all mean. Determine the standard deviation of your data points by using this command: "Standard deviation: =STDEV(data points)."
- 3). Tally the upper and lower control limits (UCL, LCL). Enter this formula: "UCL = CL + 3*S", "LCL = CL -- 3*S." This conveys 3 standard deviations above and below your mean. This will process your 1, 2 and 3 sigma lines. Draw a line at each deviation you've calculated. Diagram the subgroup means "x-axis" counter to the "y-axis." Confirm that your points do not fall off any of your sigma lines. This can help you determine whether you data is "in-control" or "out-of-control."
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