Increasing returns to scale or decreasing costs arise because of technological and financial reasons. At the technological level, economics of scale arise because as the scale of operation increases, a greater division of labor and specialization can take place and more specialized and productive machinery can be used. Specifically, with a large-scale operation, each worker can be assigned to perform a repetitive task rather than numerous different ones. This results in increased proficiency and the avoidance of the time lost in moving from one machine to another. At higher scales of operation, more specialized and productive machinery can also be used. For example, using a conveyor belt to unload a small truck may not be justified, but it greatly increases efficiency in unloading a train or ship. Furthermore, some physical properties of equipment and machinery also lead to increasing returns to scale. For example, doubling the diameter of a pipeline more than doubles its capacity to transport cargo without doubling costs, and so on. Thus, per-unit costs decline. Firms also need fewer supervisors, fewer spare parts, and smaller inventories per unit of output as the scale of operation increases.