The Pythagorean cup, attributed to the ancient Greek mathematician Pythagoras, is designed to empty its contents if filled beyond a certain point. The cup has a central column with a hidden siphon mechanism. When the liquid level rises above the designated point, the siphon effect kicks in, causing the entire contents of the cup to drain out through the bottom.

This market resolves to the odds at close, plus 34%, looping back around to 0% after 100%. A more concise formula:

R = (O_c + 34%) mod 100%

Initially one is incentivised to bet it up, but if too many people do so, it becomes easier and thus more likely that someone will tip it over the spillover point (66%) at the last second (e.g. trolls trying to make everyone mad, or users making deals with each other to profit from simultaneously betting it down), and vice versa if people overcompensate.

34% was chosen so that it won't be profitable for a whale to swoop in and bet it from just below the spillover point down to 1%, as it would with smaller resolution offsets.