NOTE: The single item should not have the cost entered, only the selling prices.
The system
will automatically update the cost price of the sub-item when the bulk item is purchased.
The unit cost
prices for these items are automatically calculated by taking the pack size of the broken pack item and
dividing it by the main item's pack size,
and multiplying it by the unit cost of the main/bulk item.
The "Primary Cascading Order Item" in the right highlighted block tick is only necessary if you are making use of ordering formulas under the Ordering tab.
Also, remember not to create any order formula under the single item in the Ordering tab.