A trading system that cannot explain its balances to the cent will eventually make decisions on wrong numbers. This guide shows how we keep an internal double-entry ledger for trades, fees, funding and transfers, reconcile it with exchange balances, and handle the differences we find.
Our perpetual futures bot reported a monthly PnL 6 percent higher than the exchange's account history. It ignored trading fees on some fills, never recorded funding payments, and valued open positions at last trade price instead of mark price. Building PnL from the income ledger fixed it.
Our bot believed two orders were still open when they had filled hours earlier. The exchange closes websocket connections after 24 hours; our reconnect logic resubscribed but never checked what happened while disconnected. Reconnect with backoff plus REST reconciliation fixed the state drift.