Repair charges include the costs of labour and spare parts. They are generally related to the purchase value using coefficients calculated from surveys among manufacturers and repairers in industrialized countries. Estimated useful life and repair coefficients for some agricultural machines. Coefficients must be adjusted according to the nature of the work undertaken by the equipment when in operation. For more accuracy they can be easily verified in the field for different types of work.
Lubricant consumption is calculated from the engine consumption.
For tractors and combine harvesters, oil changes for the gearbox, axle and hydraulic system must be taken into account. Many such projects have disappeared because they were unable to incorporate sufficient reserves for amortizement. Estimating the annual working time is of upmost importance. For a tractor one generally allows 1000 working hours. The stock of spare parts must be carefully examined because it corresponds to locked-up funds.