Buried services with rubber ring joints are restrained by concrete thrust blocks at bends, junctions, dead ends, valves, reducers, significant changes of direction and steep grades or as the manufacturer requires, bearing on undisturbed ground, designed so hydrostatic thrust does not exceed soil or pipe capacity, not loading other services, and cured before the line is charged (2003 text).
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.