Functional-based product costing assigns only manufacturing costs to products. Exhibit
4-1 shows the general functional-based product costing model. Assigning the cost of
direct materials and direct labor to products poses no particular challenge. These costs
can be assigned to products using direct tracing, and most functional-based costing systems
are designed to ensure that this tracing takes place. Overhead costs, on the other
hand, pose a different problem. The physically observable input-output relationship that
exists between direct labor, direct materials, and products is simply not available for
overhead. Thus, assignment of overhead must rely on driver tracing and perhaps allocation.
Functional-based costing first assigns overhead costs to a functional unit, creating
either plant or departmental cost pools. Next, these pooled costs are assigned to
products using predetermined overhead rates based on unit-level drivers