1. Open Cover.sta example data from "File | Open Examples" | Datasets folder

2. Select "Statistics | QC Charts | Individuals & moving range" and click "OK"

3. Click "Variables" to select "WIDTH" as Measurements and click "OK"

4. Click "OK" to produce the X and Moving R chart and the X/MR results dialog will be also prompted

5. Under X/MR results dialog, click "Options" to access Options dialog

6. Under "Options | Stats", select "N", "Mean", "Std.dev." (N: number of the observations in the data, Mean: mean of the observations, Std.Dev: Standard deviation of the observations) and click "OK"

7. Return to X/MR results dialog and click "X" to create a compound graph containing an individual (sample size 1) chart plus a histogram of individual observations.

The Std Dev (2.3947) displayed in the top left Statistics text box (requested via Step 6) computes the standard deviation of all observations. To verify the result, select "WIDTH" and obtain its summary statistics via "Statistics | Basic Statistics | Descriptive Statistics". The standard deviation will be the same.

The Sigma (2.1094) in the chart = Averaging moving range (amr) / d2 where d2 differs by sample size. Using average of moving ranges to estimate standard deviation of the example data: sd=amr/d2 = 2.3802/1.128379=2.1094. As such, different computation methods result in different results between Std Dev (2.3947) and Sigma (2.1094).

Note: Click here to learn more computation details of IQC charts in our online help document