Tractors and machinery have evolved to high technical levels, however this advanced level of technology results in system complexities making it difficult and expensive to further improve quality. Also, it may be more difficult for farmers to realize the total potential of these higher quality systems. Computer models are powerful aids for identifying and evaluating the numerous machine and operational parameters that affect tractor and implement efficiency. They can allow engineers to optimize their design more cheaply and quickly than by using field trails only, and they can also show them which system parameters must be displayed to the operator to enable him to make best use of the total potential that is engineered into the system and for which the farmer has paid. The models introduced and explained in this paper help to analyze technical and agricultural parameters, such as soil condition, ploughing speed and depth, wheel load. In the foregoing ploughing as one of the most time and fuel consumption tillage operations was used to show how, by computer models, the influence of different technical and agricultural parameters on field capacity, fuel consumption or work time can be evaluated. As a matter of economics the extent of the models discussed had been matched to the questions posed. While the first examples were related to technical parameters the last examples showed how non technical parameters e.g. the skill of the driver, the farm structure or the farm management can greatly influence the success of farming even if the technical parameters are equitable.