Accountability asks whether an action can be attributed to the entity responsible for it. A measure relates attributable actions to the actions recorded. Attribution needs identity, time and context. A log line with a shared service account attributes nothing. The measure is about the proportion of actions that can be traced to a person or a system with a named responsibility. It differs from non-repudiation: accountability does not need a cryptographic proof, but it does need a reliable identity and a record that cannot be silently rewritten.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.