How Betfair BSP works: Before a race, bettors submit SP bets — backs that accept any price, and lays with a maximum acceptable price. At the off, Betfair runs a Dutch Book algorithm to find the clearing price: the highest price at which total lay volume (red curve) still covers total back stakes (green line). Where they cross is the SP. Bets above the clearing lay limit go unmatched. The chart builds in real time as bets arrive, then the scanner sweeps right-to-left to find the crossing point.