In a given company there may be a significant amount of labor-related overhead,machine-related overhead,material-related overhead,or some combination of these. Any combination of two or more raises the possibility of using two or more overhead allocation bases. Further,some components of factory overhead cost may not be closely related to the usage of labor,machinery,materials,or any other measure of production volume. They may be related to activities or transactions such as the number of setups or the number of product design changes,neither of which is a measure of production volume. Costing systems that include one or more non-volume-related factors among the bases used for allocating overhead are called activity costing systems and are discussed in chapter 13. The remainder of this section deals only with volume-related allocation bases.