Why it works: you cannot see this on one question. Any single confident wrong answer is bad luck, and everyone has a story explaining it. Across a dozen calls the pattern stops being deniable — and it is almost always the same pattern, which is that 90 means about 70. That gap is why plans slip, why estimates are optimistic, and why the escalation nobody thought was likely happened anyway.
Works alone, or with a room agreeing each call out loud. The argument about the number is worth as much as the number.