An allocation base, such as direct labor hours, direct labor dollars, or machine hours, is used to assign manufacturing overhead to individual jobs. Which one is NOT a reason why we use an allocation base because. Many types of manufacturing overhead costs are fixed even though output fluctuates during the period. OA B Manufacturing overhead costs, which are not directly allocated, become variable costs. Manufacturing overhead consists of many different items ranging from the grease used in machines to the production manager's salary. . It is impossible or difficult to trace overhead costs to particular jobs. OD