Look into the data quality issues that monitoring, users and measurement bring up, to understand what they are, how often they occur and what they cost; this opens the Check stage, in which 5.1 has data quality and process performance measured against the strategy and requirements and the results reported. ISO 8000-62 assigns it to maturity Level 4 (Predictable).
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.