Unit Price / Best-Value Comparator

Inspectable records

Ledger state

The current ledger marks this instrument verified clean within the source-bound verification corpus.

Area

Everyday & Life

Tranche

tranche-5

Evidence ID

t5-082

Ledger rows

1

No ledger note is attached.

Review findings

The arithmetic formula is standard, but the specification is not complete enough for unambiguous implementation. Exact ambiguities requiring review are the conversion-factor source, target-unit selection, currency handling, invalid-unit behavior, precision and tie-breaking rules, and the meaning of "best value." An honest label should state that the instrument computes lowest price per comparable unit only; it does not assess quality, quantity suitability, nutrition, or total consumer value.

Formula and scope findings

• The division formula is correct only when every quantity is expressed in compatible units and every price uses the same currency.
• The phrase "normalized to same unit" does not specify conversion factors, a target unit, or handling for incompatible units.
• "Best value" is ambiguous: the formula ranks lowest monetary cost per quantity, not overall product value, quality, or utility.
• No rounding or tie-breaking rule is specified for displayed unit prices and rankings.

Unit assumptions

• All prices in a comparison use the same currency; test vectors use USD.
• Quantities are positive and represent comparable amounts of the same product dimension.
• Unit conversion is exact or uses an explicitly defined conversion factor; the target unit is selected before comparison.
• A lower price per normalized unit is ranked as better value.
• Prices and quantities are treated as numeric values before display rounding.

Boundary hardening

BREAK_CLAIMED · SELF_FLAGGED

A zero quantity produces an undefined division, and mixed units require an explicitly defined normalization branch. Without validation and unit conversion, the comparator can produce undefined results or an incorrect ranking.

Errata and corrections

No applied erratum is attached to this unique-name record.

Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

{
  "inputs": {
    "options": [
      {
        "id": "A",
        "price": 5.98,
        "quantity": 2,
        "unit": "L"
      },
      {
        "id": "B",
        "price": 3.29,
        "quantity": 1,
        "unit": "L"
      }
    ],
    "target_unit": "L",
    "currency": "USD"
  },
  "expected_outputs": {
    "unit_prices": [
      {
        "id": "A",
        "price_per_unit": 2.99,
        "unit": "USD/L"
      },
      {
        "id": "B",
        "price_per_unit": 3.29,
        "unit": "USD/L"
      }
    ],
    "ranked_best_value": [
      "A",
      "B"
    ]
  },
  "working": "A: 5.98 USD / 2 L = 2.99 USD/L. B: 3.29 USD / 1 L = 3.29 USD/L. Since 2.99 < 3.29, ranking is A first, then B."
}

Related workflows

No source-defined multi-instrument workflow membership is recorded.

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json · VERIFIED_CLEAN
• evidence-tranche5/tranche5-results.json
• BOUNDARY_HAZARD_CATALOG.json