In traditional costing systems indirect costs are grouped together into cost pools. From there they are then allocated to cost objects in proportion to direct labor/machine hours, or direct materials consumed, also known as volume-based cost drivers. Since many of these indirect costs are not really used by products in proportion to their production volume, this allocation is often arbitrary. As a result, traditional costing systems lead to inaccurate calculations of product costs. (Drury 1994). Figure 1 illustrates the allocation of indirect costs in traditional costing systems.