Final answer:
Slightly different weights of candy bars within control limits represent common cause variation, which is expected in a stable process. Special cause variation, on the other hand, indicates an issue in the process, such as equipment needing recalibration.
Step-by-step explanation:
The slightly different weights of candy bars within control limits represent a type of variation known as common cause variation. This variation is inherent in the production process and is expected to occur even when the process is under control. Common cause variations are caused by many small, random factors that are always present in the system and are generally acceptable, as long as the variations remain within the predefined control limits set by the process.
In contrast, if the variation exceeds control limits or is not random, it may be due to a special cause variation. This occurs when an identifiable factor causes the variation, such as a malfunctioning piece of equipment or an error in the process. In the scenarios provided in the question, the concern about cereal box weights exceeding the standard deviation indicates a potential special cause variation that could require recalibration of the filling machine.