Plastic dog tags are being produced in a company named Dog Tag Plastics. The plastic material is first molded and then trimmed to the required shape. The curetimes $($which is the time for the plastic to cool$)$ during the molding process affect the edge quality of the dog tags produced.

The aim is to achieve statistical control of the curetimes using X$-$bar and R$-$charts.

Curetime data of $25$ samples, each of size four, have been taken when the process is assumed to be in control. These are shown as follows.