Approach
One family, from each legal conversion date
ECI FX does not treat vanished notes as souvenirs. It continues each legacy unit as a rate in a single family: legal at adoption, then quoted together so a desk can make, list or stream them as one book.
Where each name starts
On the day a country adopts the euro, the rate is the irrevocable conversion factor in Council Regulation (EC) No 2866/98 as amended — public law, not a market print. The Deutsche Mark converts at 1.95583, the French franc at 6.55957. That is the floor of the product, not the product.
What happens after adoption
Each currency then lives inside the family. France is not Germany; names are allowed to differ, but they are not allowed to fall apart into 21 unrelated indices with euro labels. Daily moves keep the same relative pattern across the family after adoption. The size of those moves is restored to the historical scale of Europe’s legacy rates versus the euro before 1999, so gaps versus the euro, versus the dollar, and versus each other remain visible. How the pattern is formed is licensed methodology, documented for counterparties under NDA and contract — not on this website.
Three numbers, three jobs
- Official history — published market rates versus the euro (and the ECU before 1999) until each legal conversion, then the ECI family from that date, shown as an index of 100 at conversion.
- Live theoretical mid — an intradaily indication for desks. It is not executable and is not a fixing.
- Your market — bid, ask, credit and inventory stay with the dealer or venue.
For counterparties
Market makers, exchanges and liquidity providers receive the specification, lineage and operational controls with the commercial feed. This site is the public window: quotes, history, and a way to start that conversation.