Unit Coverage
How much of a decision surface's units were declared, and how much of the checking that makes possible actually ran (§4.2.4, G.9 row 7).
unit is optional, so every check built on it is conditional on someone having declared one. That is a defensible design and an easy one to let rot: a surface where nothing declares a unit passes every unit check trivially, and looks identical in a green test run to one where every check fired. This type is what makes the difference visible, and it is the answer to D.10's objection that a field documenting an unenforced invariant is a fault — the invariant is enforced where it can be, and the coverage of that enforcement is reported rather than assumed.
Constructors
Properties
Constraints where every summed lever declared a unit, so the sum was fully checked.
Constraints where only some did — checked in part, and knowingly so.