CJV-MTH-1.0 — Evidence-Graded Product Carbon Claim Registry: Specification

This document specifies a way to make product-level carbon claims checkable rather than merely asserted. Its unit of account is a verified unit: one batch, one fixed boundary, one functional unit, one ledger entry and one recomputable hash. The specification defines: five properties a unit must satisfy to count as verifiable; a grade computed from the share of the footprint that is metered rather than estimated; a rule that the counterfactual baseline must be co-signed before the improvement is claimed; four machine-readable refusal classes; an append-only hash-chained register that a third party can recompute without trusting the issuer; and a partition between what an evidence layer may state and what requires a countersignature from an accredited body. It is published for citation and review. It is not an accredited standard, not an ISO/IEC deliverable, and it confers no certification. The author is also the operator of the platform and registry described; the organisation that would demonstrate independence has not yet been established, and no signing partner is contracted. Version 1.0 is accompanied by the register snapshot it describes (20 records, head hash 54980f3d) and a dependency-free verification script that reproduces every hash.