Using the part 1 terms (3.21), the device is broken down as a hierarchy: the whole chip is the component, a block one level down (a processor core, say) is a part, lower blocks (its register bank) are subparts, and the smallest units analysed (individual registers with their logic) are elementary subparts; how far down to go, and what counts as elementary (a single flip-flop, one analogue transistor), is chosen according to the safety concept, how far the analysis has progressed and where the safety mechanisms sit, inside the chip or at system or element level.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.