Situation A. The company builds wood book cases. The company has on its bill of materials one pint of glue, in addition to the wood and other raw materials. The company charges the glue as a direct cost because it's used on every bookcase and is listed as a raw material.

Situation B. The company builds wood book cases. The company keeps glue as a supply for the production department and processionally uses some glue on the bookcase. Most of the wood shelves are connected using wood screws. This company list the glue as a supply as it's not frequently used.

what other situations could a direct cost become a variable or mixed cost? Please share your thoughts!