The unit is a rate across a fixed prompt set, per engine, rerun on a cadence. Not a position, because there is no position, and not a single blended score, because blending four engines hides the only finding that tells you what to do next.
Record four things per question per engine: whether you were named, whether you were linked, who was named instead, and which sources the answer drew on. Named and linked are separate outcomes with separate fixes. The competitor named in your place is reliably the line that gets forwarded internally.
Three things to be suspicious of. A screenshot presented as evidence, since generative answers vary between runs and one ask is one sample. A single AI visibility score with no per engine breakdown. And any precise revenue figure attributed to AI search, because assistants pass very little referrer data and traffic that started in an answer usually arrives looking like direct. Anyone quoting that number is modelling, and the honest version of the claim names its assumptions.
Then hold the deterministic half separately, because it is the half that is actually verifiable. Crawler access per bot, render output, schema validity, freshness and attribution signals do not vary between two samples, any third party can check them on your live pages, and they are what you point at when somebody asks whether the work was real.