Robin Hanson introduced me to it. It does ask about things for which you have no information, which is why it is about calibration. You draw a card with a question with a numeric answer. Everyone publicly guesses at the answer. You then wager on whose answer is closest without going over. It's a good demonstration of the effectiveness of recalibration. It's also about expected value, because your wager gains you more points if you wager on an answer far from the median, so you need to trade off confidence vs. expected returns.