Dimensions are in millimetres unless stated and are net: skirtings, kerbs, handrails and other fixtures may not reduce them. They are measured to finished surfaces such as tile faces and finished floor surfaces, and limiting dimensions for inclined surfaces on the accessible path are taken horizontally and vertically. The 2021 preview notes advise allowing for construction tolerance when setting out.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.