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

instrument implementation / implementation-contract

# Unit Price / Best-Value Comparator implementation

A source-bound implementation contract for Unit Price / Best-Value Comparator; deployment and executable qualification remain separate.

Status: **VERIFIED_CLEAN**Lifecycle: **implementation-contract**

## Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

**Record owner**: Guth Instruments

**Lifecycle**: verified-clean

**Evidence ID**: t5-082

**Effect**: Computation or source lookup only

## Input and validation requirements

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.

## Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

## Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

````
{
  "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."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/unit-price-best-value-comparator/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/unit-price-best-value-comparator/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/unit-price-best-value-comparator/qualification/>)

## Sources and evidence

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

- `VERIFIED_LEDGER.json`

- `evidence-tranche5/tranche5-results.json`