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

instrument mechanism / verified-clean

# Unit Conversion Cost Comparator mechanism

The inspectable method record for Unit Conversion Cost Comparator, kept separate from implementation and qualification.

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

## Model scope

The core arithmetic is standard, but the specification needs explicit unit metadata and conversion rules, currency and price-treatment assumptions, validation constraints, rounding behavior, and tie handling before it can be approved.

- The algebraic formula unit_price=price/quantity is correct only after quantity has been converted to the target unit.

- The specification does not define source units, conversion factors, or the normalization procedure, so the phrase quantity(normalized to common unit) is ambiguous.

- The specification does not define whether cheapest-option comparisons use exact values or rounded displayed unit prices, nor how ties are reported.

- The formula is not valid for incompatible quantity types, such as comparing weight to count, unless an explicit equivalence is provided.

## Units and conventions

- All prices in a comparison are denominated in the same currency, here assumed to be USD.

- Prices are assumed to include the same treatment of taxes, discounts, deposits, and fees; otherwise the comparison may be misleading.

- Quantity units are explicitly supplied and converted to the target unit before division.

- Currency-per-target-unit outputs are shown to at least two decimal places, while cheapest-option selection should use unrounded values.

- Mass conversions use 1000 g = 1 kg; volume conversions use 1000 mL = 1 L; ounce examples use the same ounce definition for both products.

## Inspectable vector

One of 4 source-bound review vectors:

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

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

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.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/unit-conversion-cost-comparator/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/unit-conversion-cost-comparator/implementation/>)[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`

- `BOUNDARY_HAZARD_CATALOG.json`