Petroleum is cracked to make gasoline and other products such as lubricating oil and kerosene.

Petroleum is cracked to make gasoline and other products such as lubricating oil and kerosene. The process is too slow to allow sample sizes greater than one. The following are the octane rating of the output from the process recorded at intervals of thirty minutes each. 

Obs. Number Octane rating 

1 86.0 

2 88.0 

3 86.0 

4 85.0 

5 86.0 

6 88.0 

Compute the control limits of appropriate control charts, which can be used to monitor the process. Use alpha = 0.0026.