Soil around excavations can change quickly as it dries out, as the water table shifts or as it becomes saturated. A competent person should check the soil and the condition of shoring, batters and trench walls often for fretting, slipping, slumping or swelling. Where needed, the excavation should be repaired or the shoring strengthened from above before work below ground continues.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.