According to the PMI, there are four main categories of project costs that need to be documented: direct costs, indirect costs, fixed costs, and variable costs. Each category has its own characteristics and implications for the project budget and cost control. Direct costs are those that are directly attributable and allocable to the project, such as labor, materials, equipment, travel, and subcontractors. They are usually easy to identify and measure, and can be controlled by the project manager. Indirect costs are those that are not directly attributable or allocable to the project, such as overhead, administration, utilities, and depreciation. These costs are usually difficult to identify and measure, and they are generally controlled by the organization or functional manager. Fixed costs do not change with the level of output or activity of the project; examples include rent, insurance, licenses, and salaries. They are predetermined before the project starts and unaffected by changes in scope or schedule. Finally, variable costs change with the level of output or activity of the project; these include materials, supplies, fuel, and hourly wages. Variable costs depend on the project scope and schedule and can be influenced by the project manager.