Lesson 19 introduced settlement netting in the bilateral case. At scale (NIBSS clearing windows, scheme net settlement, ACH multilateral netting), the same principle applies to thousands of counterparties at once. Every clearing window, a central operator nets every settlement obligation across all participants and produces ONE net debit / credit per participant. A bank with 50,000 inbound transfers and 48,000 outbound ones receives ONE wire for the net difference. Your ledger has to handle the inversion: post 50,000 individual user-facing entries (so wallets credit on time) while booking the SINGLE settlement wire against your bank account at the clearing window. This lesson walks the engineering of that asymmetry.