For loadbearing walls, lintel and ring beam sizes come from the tables for storey and roof type, with top plates over lintels and bearing per the table notes; ring beams are one depth larger than the equivalent lintel and, other than N1 and N2 tile and N1 sheet cases, sized on the greater of the opening width or tie-down spacing; gable end, concentrated load and internal wall lintels follow their own rules (a lintel is needed over openings wider than 1800 mm in non-loadbearing external walls); sill, lintel and ring beam trimmers follow the trimmer table above set opening widths and head gaps.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.