Source: https://guthlabs.ai/docs/instruments/trip-fuel-cost-calculator/mechanism/

instrument mechanism / verified-clean

# Trip Fuel Cost Calculator mechanism

The inspectable method record for Trip Fuel Cost Calculator, kept separate from implementation and qualification.

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

## Model scope

The computation is valid under the stated unit assumptions, but the catalog specification must explicitly define distance units, US versus Imperial MPG and gallons, currency, and input validation rules before receiving a PASS verdict. The honest-label note correctly states that manually entered fuel prices are only as current as the user's input.

- The algebraic formulas are standard and correct, but the specification does not define the distance unit, MPG convention, or fuel-price currency and volume unit.

- The specification does not state that MPG must be greater than zero or that distance, MPG, and price must be nonnegative.

## Units and conventions

- Test vectors assume distance is in miles, MPG means US miles per US gallon, and fuel price is in USD per US gallon.

- For the unit-conversion vector, 160.9344 km is treated as exactly 100 miles before applying the MPG formula.

- Outputs are gallons needed and fuel cost in US gallons and USD under those assumptions.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "trip_distance": 300,
    "distance_unit": "mi",
    "vehicle_mpg": 25,
    "fuel_price": 3.6,
    "price_unit": "USD/US gal"
  },
  "expected_outputs": {
    "gallons_needed": 12,
    "fuel_cost": 43.2
  },
  "working": "gallons_needed = 300 mi ÷ 25 mi/US gal = 12 US gal; fuel_cost = 12 US gal × $3.60/US gal = $43.20"
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

A zero-MPG input causes division by zero and can produce undefined mathematical results or JavaScript Infinity. Negative distance also exposes an unresolved validation/convention issue because the raw formula returns negative gallons and cost.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/trip-fuel-cost-calculator/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/trip-fuel-cost-calculator/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/trip-fuel-cost-calculator/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-tranche4/tranche4-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`