Source: https://guthlabs.ai/docs/instruments/unit-conversion-cost-comparator/implementation/

instrument implementation / implementation-contract

# Unit Conversion Cost Comparator implementation

A source-bound implementation contract for Unit Conversion Cost 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**: t5-227

**Effect**: Computation or source lookup only

## Input and validation requirements

A zero quantity makes the unit-price formula undefined. A naive plain-arithmetic implementation may emit Infinity instead of rejecting the item, allowing an invalid comparison or misleading output.

## 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": {
    "currency": "USD",
    "target_unit": "kg",
    "items": [
      {
        "name": "Item A",
        "price": 2.49,
        "quantity": 500,
        "unit": "g"
      },
      {
        "name": "Item B",
        "price": 3.3,
        "quantity": 750,
        "unit": "g"
      }
    ]
  },
  "expected_outputs": {
    "unit_prices": {
      "Item A": 4.98,
      "Item B": 4.4
    },
    "unit_price_units": "USD/kg",
    "cheapest_option": "Item B"
  },
  "working": "Item A: 500 g ÷ 1000 = 0.5 kg; $2.49 ÷ 0.5 kg = $4.98/kg. Item B: 750 g ÷ 1000 = 0.75 kg; $3.30 ÷ 0.75 kg = $4.40/kg. Since $4.40/kg < $4.98/kg, Item B is cheapest."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/unit-conversion-cost-comparator/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/unit-conversion-cost-comparator/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/unit-conversion-cost-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`