Final answer:
Observations can occur outside of control limits, tolerances, and process variability limits.
Step-by-step explanation:
If a process is performing as it should, it is still possible to obtain observations outside of control limits. Control limits are statistical limits that define the range within which a process is considered to be in control. Observations outside of these limits may indicate special causes of variation, such as equipment malfunction or operator error.
Tolerances, on the other hand, refer to the acceptable range of variation specified by the customer or the design specifications. Observations that fall outside of the tolerances indicate that the product or process is not meeting the required standards.
Process variability, sometimes measured by the process capability index (Cpk), assesses the ability of the process to consistently produce within the specification limits. If the process capability index is low, it indicates that the process has high variability and may produce observations outside of the specification limits.