When Polymarket says 70%, does it happen 70% of the time? I checked against 19.4M price snapshots. (opens in new tab)

If you trade, model, or just read prediction markets, there's one question that decides whether the price means anything: when the market says 70%, does the thing actually happen about 70% of the time? That's calibration, and it's the single most decision-relevant property of any probabilistic forecaster. A market can be liquid, popular, and heavily traded and still be systematically wrong in a way that's invisible until you score it against what actually resolved. So I built the thing that l...