qualifier number + unit a measured amount

filtration efficiency

The proportion of particles at the stated rating size that the element actually holds back — Donaldson publishes P550048 as 99% at 30 microns; MANN publishes a cabin element as removing up to 95% of soot and trapping up to 90% of gases. A qualifier of `filtration_rating`, because the number is meaningless apart from the size it is quoted at.

Filtration efficiency is a measured figure.

It is a qualifier of filtration rating — it has meaning only inside a filtration rating statement, one per statement, never on its own. It belongs with filtration rating to measurement — its measurable, physical facts.

It is answered inside every filtration rating statement, not as a standalone question on a kind.

answered with: №number + unit — a number paired with a unit drawn from an exhaustive unit vocabulary.
value domain: Percent units — the vocabulary its answers are drawn from.
qualifier of: filtration rating — one per statement — it has meaning only inside that host's statement.

Answered inside every filtration rating statement — not a standalone slot on any kind.