Final answer:
In SPC, if all sample measurements are within control limits and show no special patterns, the process is considered in control, reflecting common-cause variation. The answer is A. This does not directly comment on the quality of individual units or the overall production requirements, and process limits are typically statistically determined.
Step-by-step explanation:
When using Statistical Process Control (SPC), if all sample measurements fall inside the control limits and there are no other patterns in the samples, the correct answer is: A. if there is no other pattern in the samples, the process is in control. This means that the process variation is due to common causes and not due to special causes that could be indicative of an underlying issue with the process.
Control limits are determined statistically and help in understanding whether the process variation is natural or whether it is due to some specific, assignable cause. The presence of data within control limits typically indicates a stable process, but it does not necessarily mean that each unit manufactured is of acceptable quality (option C), nor does it suggest the process output exceeds requirements (option B) or does not fulfill the requirements (option D). Process limits can indeed be determined statistically, making option E incorrect.
The concept of control in SPC is deeply interlinked with the properties of the data collected from the process, such as the standard deviation, which is a measure of the variability of the process. As per the Central Limit Theorem, for sufficiently large samples, the distribution of sample means will be approximately normal, regardless of the population's distribution.