Final answer:
The best tool for the windshield manufacturer to verify the appropriateness of windshields' thickness is an x-bar chart, which helps monitor and control process variation over time.
Step-by-step explanation:
To ensure the windshields meet the desired thickness specifications, the best tool to adopt would be C. an x-bar chart. This statistical process control tool allows the manufacturer to monitor the process and detect any variations from the target thickness. An x-bar chart is effective in tracking the central tendency of a process over time. By plotting sample means of the thickness measurements, trends and shifts can be identified, allowing the manufacturer to intervene when the process exhibits signs of producing out-of-specification windshields.
While a process capability index and a process capability ratio are useful in assessing whether the process can meet the specifications, they are generally used after the process stability has been established. An operating characteristics curve is more relevant in the context of sampling and testing rather than ongoing process control.