The shipyard job requires 270 machine-hours. At ¥2.24 per machine-hour, the electrical cost actually caused by the job would be only ¥604.80. This contrasts with the electrical cost of ¥3,171 under the old cost system and ¥2,835 under the new ABC system. Both the old cost system and the new ABC system grossly overstate the electrical costs of the job. This is because under both cost systems, the large fixed electrical costs of ¥63,528 per week are allocated to jobs along with the electrical costs that actually vary with the amount of work being done. In practice, almost all categories of overhead costs pose similar problems. As a consequence, the costs of individual jobs are likely to be seriously overstated for decision-making purposes under both traditional and ABC systems. Both systems provide acceptable cost data for external reporting, but both provide potentially misleading data for internal decision-making unless suitable adjustments are made.
6. Electricity is used for heating, cooling, and lighting the building as well as to run equipment. Therefore, consumption of electrical power is likely to be affected at least by the weather and by the time of the year as well as by how many hours the equipment is run. (Fewer daylight hours mean the lights have to be on longer.)