Ratio corridors: a table nobody has to negotiate

A corridor used to start with two banks agreeing a list of price edges for one product, ratifying it, and renegotiating it whenever the market moved. A risk committee cannot easily sign off on detection that depends on a table co-authored with a competitor, and every corridor began with a meeting about Mirror.

A ratio corridor removes the negotiation. Each leg bands the ratio of its price to a public reference figure, against a ratio table published once for every corridor. The only choice specific to the corridor is which public figures make the reference, and that is a citation, not a price.

How a corridor opens#

Pick a published ratio table. The tables are protocol constants, closed by construction:

Table	Edges (price ÷ reference)	A clear at tolerance 0 stands for at most	At tolerance 1
`ratio-5`	0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15	1.06x	1.18x
`ratio-10`	0.85, 0.95, 1.05, 1.15	1.12x	1.36x
`ratio-20`	0.7, 0.9, 1.1, 1.3	1.29x	1.86x

Cite the reference. List 1 to 8 public sources, each by publisher, instrument, publication, basis, currency and unit. A source never carries a figure. Set a quorum (how many sources must report), a spread (how far apart they may be), and the date rule that picks the figures for a shipment.
One bank opens it; the other accepts it. The proposing bank signs a corridor.propose with the table, closed: true, a ceiling of at most 1.5x, and the reference set. The other bank runs mirror-bander accept, which shows exactly what it is accepting and refuses anything outside the shape the operator admits. Nothing is co-authored.
Band. Each party, including a customs office if one witnesses the corridor, fetches the same public files itself and runs mirror-bander band --reference-set set.json --reference-figures figures.json --basis USD,t,CIF,Rotterdam.

What happens inside the bank#

R is computed exactly. It is the median of the cited figures, refused if fewer than the quorum report or if they disagree beyond the spread. A reference the sources dispute judges nothing.
The price is divided by R, by banding the value against the quantity times R, computed exactly. The leg's commitments are ordinary commitments: the operator, the verifiers and the conformance vectors are unchanged.
Only hashes leave. The figures' file hashes ride inside the committed pricing basis. Neither R nor any figure leaves the bank.

What a clear means here#

On ratio-10, both legs were within 0.85 to 1.15 times the public reference, in the same band, so they differ by at most 1.12x.
An off-market price never clears. A price more than 15% off the reference lies outside the closed table. It commits markers that match nothing, so it reads divergent and goes to review, even when every party states the same number.
Two references never clear against each other. Two legs divided by different files read basis_mismatch.

One bank, on day one#

A bank with no counterparty on the rail yet can still run its own book against the public reference:

mirror-bander screen --in legs.csv --reference-set set.json --reference-figures figures.json

It counts how many prices sit below, inside and above the table, computed inside the bank, submitting nothing and naming no shipment. Those counts are a per-corridor case the bank can take to a counterparty without disclosing a single trade.

The honest limits#

The reference is the new attack surface. A launderer can try to move the benchmark instead of the trade. A median of distinct publishers and the spread refusal make that harder; they do not make it impossible.
Some goods have no credible public reference. Services, bespoke goods and thin niche markets cannot have a ratio corridor. They keep a negotiated closed table, and some of the highest-risk trade sits exactly there.
Many benchmarks are licensed. Each bank fetches the cited figures under its own data licence. Mirror never fetches, holds or publishes a figure.
A clear is not a fair-value opinion. A reference prices a standard grade at a stated basis, as its citation says.

For implementers#

The normative text is §3.1 of the specification. The conformance pack includes ratio_reference and commit_leg_ratio. The whole flow — opening, accepting, banding, clearing on a customs office's word, refusing an off-market price and a mismatched reference, and the one-bank screen — runs locally with node server/ratio-corridor.test.js.