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The certificate is the factory’s unit of trust — the answer to the governing question any operator must face: when this breaks in production, who takes the call? The factory does, and the certificate is the artifact that makes that answerable. A Certificate of Conformance — the lot number — is a signed, versioned record issued at Station 4:

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Not a badge — a claim with an expiry

A certificate attests that a specific unit, with a specific bill of materials, passed specific verification against a specific work order, on a specific date. Every word of that sentence is load-bearing, and the last one is why certificates expire: the unit’s quality is a distribution over future runs, and the world under it drifts (Thesis 2). A unit without a certificate is not finished; the certified unit — artifact plus certificate — is the factory’s unit of production. The builder does not certify. Verification is independent of generation (Station 3), and the signature at Station 4 is human acceptance of the claim and its evidence — one of the line’s two takt-bound touches.

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What a certificate buys

Full traceability comes free: any field defect walks backward from certificate to BOM to part to die, so the fix lands on the die — the template, the part process — not on the single unit. Fleet response becomes a query: a model swap reopens every certificate that binds that model; the BOM makes this a lookup, not an investigation. Early invalidation is defined, not improvised: the expiry field names its own triggers. Certificates live in git alongside the units they attest. The certificates are proof you can sleep.

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The shelf: certificates issued

Every certificate below is a live record, not a sample. Each page renders the real card, the content-hashed bill of materials, the evidence with its actual numbers, the liability chain, and the expiry with its triggers. Two of the four carry a published defect: that is the point, not an embarrassment. A factory that hides its escapes is selling permanent trust, which nobody honest sells.

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Self-audit