X Bar- and R-charts Example

The following example uses the Coating.jmp data table. The quality characteristic of interest is the Weight column. A subgroup sample of four is chosen. An X-chart and an R-chart for the process are shown in Figure 3.17.

Select Help > Sample Data Library and open Quality Control/Coating.jmp.

Select Analyze > Quality and Process > Control Chart > XBar.

Note the selected chart types of XBar and R.

Select Weight and click Process.

Select Sample and click Sample Label.

Click OK.

Sample six indicates that the process is not in statistical control. To check the sample values, click the sample six summary point on either control chart. The corresponding rows highlight in the data table.

Note: If an S chart is chosen with the X-chart, then the limits for the X-chart are based on the standard deviation. Otherwise, the limits for the X-chart are based on the range.

Figure 3.17 Variables Charts for Coating Data

Right-click in the XBar of Weight plot and select Chart Options > Box Plots.

Double-click on the Y axis (Mean of Weight) and change the Minimum value to 16, then click OK.

Figure 3.18 Box Plots for Coating Data

The box plots in Figure 3.18 show that the sixth sample has a small range of high values.