Moldflow uses occurrence numbers to indicate the symmetry of a model. Consider the following example:
A four-cavity mold exists, which requires that only one cavity is modeled in Moldflow. However, the mathematical modeling concept of symmetry, such as representing only a quadrant of the pipe for the sprue, is not used. Instead, the sprue is represented by a full pipe and the occurrence number accounts for the fact that there are four parts and only one sprue, as shown below.
If you consider an eight-cavity mold, it becomes apparent why standard symmetry arguments do not apply and occurrence numbers are needed.