The Data Collection Areas

In this exercise, we are actually using a specialisation of the XmR chart, often called a Deviation from Aim Chart. This type of chart is used when you want to monitor how far away each sample value is from its target value. The X value recorded on the chart is the difference between the actual value and the target value. The chart is plotted in exactly the same way as a standard XmR chart, but the data recording area has extra boxes where the sample values and the targets can be recorded. This preserves more information about the process than if only the calculated X values were to be recorded.

The required headings have been added to the recording boxes:

• the X box will be used to record the value Actual Time - Estimated Time
• the mR box will be used to record the moving range, which is the difference between successive values of X

The remaining areas on the chart are used to record any additional remarks and for calculating the control limits for the graphs. Calculating control limits is beyond the scope of this course, so you needn't worry about this section.