The moving range (MR) Chart is used to monitor and detect changes in process variation when your data are individual measurements. Each plotted point, or moving range, is simply the absolute value of between two consecutive measurements. The MR chart helps you to determine whether there has been a sudden change in your process.

·    An in-control process exhibits only random variation within the control limits.

·    An out-of-control process exhibits unusual variation, which may be due to the presence of special causes.

A liquid detergent company wants to assess whether or not its process is in control. The liquid detergent is made in batches by mixing together a number of ingredients. The quality characteristic of interest is the pH value for each batch. Measurements of the pH value for 25 consecutive batches were taken.

Data: Detergent.MTW (available in the Sample Data folder).