Constructing an Chart Based on Standard Deviations An chart based on standard deviations (instead of ranges) is made by plotting sample means with a centerline at and control limits at 1 A3 and 2 A3 , where A3 is found in Table 13-2 and is the mean of the sample standard deviations. Use the data in Table 13-1 to construct an chart based on standard deviations. Compare the result to the chart based on sample ranges (shown in this section).