How it goes

1. You open a room and put the join link on the wall. Everyone scans it and gives a name.
2. You ask a question with a number for an answer. How many lamp posts are there in Munich? When was the first one lit?
3. Everyone sends a lower and an upper bound from their phone.
4. You stop taking ranges, and the room talks it over.
5. You ask for a second range. Each phone starts from that player's first answer, so submitting it unchanged counts as an answer.
6. You reveal. Everybody sees the answer, the room's numbers, and how far the discussion moved them.

Why ranges, and why twice

A single guess is almost always wrong, and knowing it is wrong tells you nothing. A range is a claim about how much you know: if you are ninety per cent sure, then nine of your ten ranges ought to contain the answer. Too few and you are overconfident, which is the usual case. Ten out of ten and your ranges are wider than they need to be.

Asking twice measures something else. The difference between your two ranges is how much the discussion moved you, and the room can see whether the second answers were closer to the truth than the first.