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

instrument implementation / implementation-contract

# Trip Fuel Cost Calculator implementation

A source-bound implementation contract for Trip Fuel Cost Calculator; 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**: t4-103

**Effect**: Computation or source lookup only

## Input and validation requirements

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.

## 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": {
    "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"
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/trip-fuel-cost-calculator/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/trip-fuel-cost-calculator/mechanism/>)[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`