Source: https://guthlabs.ai/docs/instruments/unit-price-best-value-comparator/

instrument / verified-clean

# Unit Price / Best-Value Comparator

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

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Inspectable records

[01**Overview**Purpose and lifecycle](<https://guthlabs.ai/docs/instruments/unit-price-best-value-comparator/>)[02**Mechanism**Method and assumptions](<https://guthlabs.ai/docs/instruments/unit-price-best-value-comparator/mechanism/>)[03**Implementation**Binding and validation](<https://guthlabs.ai/docs/instruments/unit-price-best-value-comparator/implementation/>)[04**Qualification**Evidence and errata](<https://guthlabs.ai/docs/instruments/unit-price-best-value-comparator/qualification/>)

## 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`