A manufacturer of hair products needs to monitor the pH of its shampoo. The normal pH of hair is slightly acidic, in the range of 4.5-5.5. To maintain hair strength and vitality, shampoo and conditioning products should be pH balanced with hair. In order to ensure quality, six separate output batches are measured at regular time intervals and their pH recorded.

This information is collected in shampoo_ph.sav. Use control charts to monitor this process with X-bar and R charts.