Perpetual Engine Series Part 2: Real-Time PnL Calculation 📈

In Part 1, we explored Liquidation Logic —the safety net that prevents exchange insolvency. But for that safety net to work, the engine needs a precise, real-time "heartbeat." That heartbeat is PnL (Profit and Loss) . Get this calculation wrong, and traders lose money unfairly. Get it right, and the system stays trustworthy at scale. Here’s how I built a PnL system in Rust that handles thousands of updates per second with zero rounding errors. 1. What is PnL? (The Engine's Core Metric) PnL is simply the measure of how much a position has gained or lost. In a perpetual engine, PnL isn't just for a pretty dashboard; it is a critical input for: Liquidations: Triggered when PnL drops and erodes the margin buffer. Funding: Periodic payments deducted directly from or added to PnL. Risk Management: Monitoring the exchange's total liability and exposure in real-time. 2. Long vs. Short: Directional Profit Position direction flips the math entirely. If you're Long, you profit as the price climbs