Public evidence

engineering.conformity.z_score

Machine-checked verification for calculation version 1.0.0 · tier engine_tested

Open calculator API Capability Download JSON MCP Review policy

Verification

13/13 calculation tests · Production surface contract 4/4

Golden tests 0 / 0
Boundary tests 7 / 7
Property tests 6 / 6
Production surface contract 4 / 4
Engine tested Yes
Source checked Yes
Artifact integrity PASS
Production attestation Embedded snapshot: STALE · Last attested schema matched 1.0.0 snapshot / local build · Semantic contract ✓ · Last attestation PASS · current evidence changed · re-attestation required · Public/cache ✓ · Origin ✓ · Live production status PASS (0 stale; 164 CURRENT) @ 2026-09-16T06:44:24.909Z
Semantic contract PASS
Evidence attested at 2026-09-16T06:44:24.203Z
Last production check 2026-09-16T06:44:24.203Z
Public / cache PASS
Origin PASS
Supplemental domain review Not performed
Named expert review Not performed

release artifacts aligned PASS
schema valid input executes PASS
engine success output validates schema PASS
schema rejects incomplete input PASS

Fingerprint sha256:005a98a05f53b8cdb1bff1075587cee01ef5f939a82532b366567b123540b02b

Input schema sha256:1ca7ba0fb6016aa4f507ff8568cab586fcea65c280bc706c349ee11c8709573e · Output schema sha256:12efc0644dce8415be865db4c2685908258aae5b3a6fb870f64d24b6e8f5a547 · Build-time SHA-256 digests prove published artifacts agree with each other (release_integrity.scope=workspace). Production attestation GETs canonical URLs twice (public/cached view and origin), including Capability HTML, via npm run attest:production --write (published at /.well-known/calculatorx-production-attestation.json) and fails if the public Capability page advertises a different calculation_version. This is artifact consistency, not an independent immutable release log.

Build & scope

Engine identity and declared limitations.

Tool: z-score
Engine: z-score
Engine build: 2026-09-16
Evidence core: 2026-09-16T21:07:40.795Z
Rendered: 2026-09-16T22:38:08.853Z
Last reviewed: —

Assumptions

ISO 13528 z-score with scheme SDPA σ_pt
|z| ≤ 2 is pass; 2 < |z| < 3 is warning; |z| ≥ 3 is fail
Not zeta (lab u), not En (expanded U), not TUR, and not an ILAC G8 spec decision

Limitations

σ_pt is the scheme SDPA — this page does not compute lab u or U = k·u
Not the zeta-score (that uses √(ulab²+uref²))
Not the normalized error En (that uses already-expanded U)
Not TUR and not an ILAC G8 specification decision on y
|z| ≤ 2 is pass; 2 < |z| < 3 is warning; |z| ≥ 3 is fail

Sources

Standards and references supporting this tool specification. Methods are listed separately — they are algorithms, not bibliographic sources.

ISO 13528 — Statistical methods for use in proficiency testing by interlaboratory comparison — z-score z = (x − X) / σ_pt
Supports: z uses the standard deviation for proficiency assessment, not laboratory u; |z| ≤ 2 / 2–3 / ≥ 3 interpretation
ISO/IEC 17043 — Conformity assessment — General requirements for the competence of proficiency testing providers — Performance statistics in proficiency testing
Supports: z-score is a PT performance statistic distinct from En and zeta

Published checks

Golden, boundary, and property cases included in this evidence build.

ID	Kind	Status	Detail
`boundary-z`	boundary	pass	Expected z=0.5 · abs_z=0.5 · decision=pass · Actual z=0.5 · abs_z=0.5 · decision=pass · ylab=2.5 · xref=0 · sigma=5
`boundary-z-two`	boundary	pass	Expected z=2 · decision=pass · Actual z=2 · abs_z=2 · decision=pass · ylab=10 · xref=0 · sigma=5
`boundary-z-warn`	boundary	pass	Expected z=2.5 · decision=warning · Actual z=2.5 · abs_z=2.5 · decision=warning · ylab=12.5 · xref=0 · sigma=5
`boundary-z-fail`	boundary	pass	Expected z=3 · decision=fail · Actual z=3 · abs_z=3 · decision=fail · ylab=15 · xref=0 · sigma=5
`boundary-z-missing`	boundary	pass	Expected MISSING_REQUIRED_INPUT · Actual MISSING_REQUIRED_INPUT
`boundary-z-sigma`	boundary	pass	Expected VALUE_MUST_BE_POSITIVE · Actual VALUE_MUST_BE_POSITIVE
`boundary-z-ulab`	boundary	pass	Expected MISSING_REQUIRED_INPUT · Actual MISSING_REQUIRED_INPUT
`property-z`	property	pass	0.5
`property-z-two`	property	pass	2
`property-z-warn`	property	pass	warning
`property-z-fail`	property	pass	fail
`property-z-alias`	property	pass	0.5
`property-z-sdpa`	property	pass	0.5