THE CONSENSUS from the British team and most other competitors is that the basement box test is the toughest.
Here the operators must dig a square excavation 2-m wide and 1.5-m deep.
The judges then put a cubic steel frame inside the excavation to check it meets the correct dimension.
Contestants are penalised if the walls are not vertical, the base is not flat, or if there are too many teethmarks.
Points are also deducted if the machine tracks are lifted off the ground.