The unit cost of logging or road construction is essentially derived by dividing cost by production. In its simplest case， if you rented a tractor with operator for $60 per hour - including all fuel and other costs - and you excavated 100 cubic meters per hour， your unit cost for excavation would be $0.60 per cubic meter. The hourly cost of the tractor with operator is called the machine rate. In cases where the machine and the elements of production are not rented， a calculation of the owning and operating costs is necessary to derive the machine rate. The objective in developing a machine rate should be to arrive at a figure that， as nearly as possible， represents the cost of the work done under the operating conditions encountered and the accounting system in use. Most manufacturers of machinery supply data for the cost of owning and operating their equipment that will serve as the basis of machine rates. However， such data usually need modification to meet specific conditions of operation， and many owners of equipment will prefer to prepare their own rates.
The machine rate is usually， but not always， divided into fixed costs， operating costs， and labor costs. For certain cash flow analyses only items which represent a cash flow are included. Certain fixed costs， including depreciation and sometimes interest charges， are omitted if they do not represent a cash payment. In this manual， all fixed costs discussed below are included. For some analyses， labor costs are not included in the machine rate. Instead， fixed and operating costs are calculated. Labor costs are then added separately. This is sometimes done in situations where the labor associated with the equipment works a different number of hours from the equipment. In this paper， labor is included in the calculation of the machine rate.
Interest is the cost of using funds over a period of time. Investment funds may be borrowed or taken from savings or equity. If borrowed， the interest rate is established by the lender and varies by locality and lending institution. If the money comes from savings， then opportunity cost or the rate this money would earn if invested elsewhere is used as the interest rate. The accounting practice of private firms may ignore interest on equipment on the ground that interest is a part of profits and， therefore， not a proper charge against operating equipment. Although this is sound from the point of view of the business as a whole， the exclusion of such charges may lead to the development of unrealistic comparative rates between machines of low and high initial cost. This may lead to erroneous decisions in the selection of equipment.
Interest can be calculated by using one of two methods. The first method is to multiply the interest rate by the actual value of the remaining life of the equipment. The second simpler method is to multiply the interest rate times the average annual investment.
For straight-line depreciation， the average annual investment， AAI， is calculated as
AAI = (P - S) (N + 1)/(2N) + S
Sometimes a factor of 0.6 times the delivered cost is used as an approximation of the average annual investment.
Animal Rates
The calculation of the animal rate is similar to the machine rate， but the types of costs differ and merit additional discussion.
The fixed cost includes the investment cost of the animal or team， harness， yoke， cart， logging chains and any other investments with a life more than one year. Other fixed costs include the upkeep of the animals.
The purchase price of the animal may include spare animals if the working conditions require that the animal receive rest more than overnight， such as every other day. To allow for the possibility of permanent injury， the animal purchase price may be increased to include extra animals. In other cases， accidents can be allowed for in the insurance premium. The salvage cost for the animal has the same definition as for a machine rate but in the case of the animal， the salvage value is often determined by its selling value for meat. Average annual investment， interest on investment， and any taxes or licenses are treated the same as for equipment. To find the total fixed costs for the animals， the fixed costs for the animal， cart， harness， and miscellaneous investments can be calculated separately since they usually have unequal length lives and the hourly costs added together.
Animal support costs which do not vary directly with hours worked include pasture rental， food supplements， medicine， vaccinations， veterinarian services， shoes， ferrier services and any after-hours care such as feeding， washing or guarding. It could be argued that food and care requirements are related to hours worked and some part of these costs could be included in operating costs. Pasture area (ha/animal) can be estimated by dividing the animal consumption rate (kg/animal/month) by the forage production rate (kg/ha/month). Food supplements， medicine， vaccinations， and veterinarian schedules can be obtained from local sources such as agricultural extension agents.
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