Process costing accumulates costs by production process or by department Departments may exist in either job order costing or process costing, but an important distinction is that the department is the focus for cost tracing in process in costing; in job order costing, the job. batch, or lot is the focus for cost tracing. Process costing, which will be discussed in detail in Chapter 6, is used when all units worked on within a department or other work area are homogeneous, or when there is no need to distinguish among units, or when it is not practical to do so. Process costing accumulates all the costs of operating a process for a period of time and then divides the costs by the number of units of product that passed through that process during the period, the result is a unit cost. If the product of one process becomes the material of the next, a unit cost is computed for each process