C.21:4.2 - Comparison and legality rules

1. Direct same-semantics comparison. Compare readings directly when C.16’s conservative conditions hold: the same measurement definition, Characteristic, Scale and Unit semantics, compatible model and calibration regime, and compatible time or population basis. Record the admitted comparison basis. Different source labels or editions alone require no Bridge.
2. Cross-local comparison. When a comparison relies on a semantic relation between distinct F.17 local senses, cite the exact obtaining F.9 Bridge only after its predicate and dependencies hold. Keep its separate C.2.1 bounded-use claim, with the use, direction, correspondence rule, permitted-loss tolerance, and polarity, distinct from observed loss and current reliance. Follow F.9’s A.10 reliance branch or, for an actual named assurance claim, its B.3 branch for the same bounded use. If the assurance use requires an R adjustment, cite the applicable domain model and keep the adjustment in that use’s AssuranceResult. The relation supplies none of ClaimScope, measurement, comparison, or acceptance semantics.
3. Reference-plane crossing. When a reading is used across distinct world, concept, or episteme planes, cite the exact crossing basis. Any R adjustment follows the named assurance-use and domain-model condition in rule 2. A dashboard row or source label does not establish the crossing.
4. Cross-scale transformation. A conversion, normalization, distance, or aggregate names its exact Method, Scale, legal operation, and loss or uncertainty. No common scale is inferred from similar labels.
5. Freshness. A persisted or reused coordinate carries its observation window and applicable currentness rule. Staleness leads to the receiving pattern’s degrade, abstain, or reopen result; it does not rewrite the historical measurement.
6. Target bands. “Target-is-best” is not “higher-is-better.” A comparison to a band uses an explicit distance-to-band rule and leaves the G.4 threshold separate. | Scale family | Lawful ordinary operations | Prohibited shortcut | | — | — | — | | nominal status | equality, membership, mode when justified | lifecycle ranking or arithmetic without an ordered scheme | | ordinal resolution | order, median or mode where meaningful | mean, ratio, or affine arithmetic | | ratio rate or density | operations allowed by its exact Scale and Unit | unit mixing or comparison across changed construction | | interval balance | differences and target distance under its exact rule | ratios or silent target-band polarity | | entropy and concentration | operations under their own definitions | treating entropy and HHI as interchangeable or equally directed |