Maintainability covers how well the product can be modified: its modularity, reusability, analysability, modifiability and testability. The draft gives it five measure families. These are inherent measures. They read the product as built, not as used, and most of them can be collected from the repository, the build and the test suite. Modularity is about the separation of parts. Reusability is about whether an asset can be used in another context. Analysability is about the effort to diagnose a defect or a change. Modifiability is about the effort to change it. Testability is about the effort to test it. The draft gives each its own family because they fail separately: a modular product can be hard to analyse, and an analysable product can be hard to test. The measures are proxies for effort, and the draft does not set target values, so the baseline and the trend carry the meaning.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.