The purpose is to recognize and reward good model building . The primary purpose of the judges should be to evaluate the models in order to let the modeler know how well they have done and give them feedback to help them improve their skills . Most Judging categories have aspects of both difficulty and quality. Scores go up as the modeler attempts more difficult modeling projects and methods.
Scores also go up as the modeler is more successful with the chosen project and methods.
The highest scores go to the most successful results with the most difficult modeling projects and methods. Guidelines for the categories include tables with suggested scoring ranges to help in weighing the two aspects and achieving consistency. Judging then is basically positive in that points are awarded for what has been done, rather than subtracting for shortcomings compared to a theoretical perfect model. But, in practice, judging requires striking a balance between the model's good points and the model's flaws, or between what has been done and what was left undone. Your main sources of information are the entry form and the model itself.