The 1969 article argues that the number of people a manager can supervise should depend on the maturity of those supervised rather than on the level in the hierarchy: the more independent, responsible and achievement-motivated the followers, the more of them one manager can lead, in principle without limit if all are self-controlled, because control has moved from external to internal rather than disappeared. This reverses the classical rule of narrower spans at the top, since higher-level staff tend to be more mature and need less close supervision.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.