Unit Conversion Cost Comparator mechanism

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

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