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

instrument mechanism / verified-clean

# Fuel Economy Calculator mechanism

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

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

## Model scope

The two stated fuel-economy formulas are mathematically correct under their required units, but the specification is incomplete. The exact ambiguities are US versus Imperial gallons, automatic versus manual unit conversion, the missing cost-per-mile input/formula, and the undefined trend-tracking behavior. The honest label should not be 'none': the catalog should disclose that cost-per-mile and trend tracking are unsupported or require additional inputs and definitions.

- MPG = miles_driven/gallons_used is the standard formula when distance is in miles and fuel is in gallons, but the specification does not identify US gallons versus Imperial gallons.

- L/100km = (liters_used/km_driven)×100 is the standard formula when fuel is in liters and distance is in kilometers; conversion behavior for miles, odometers, or gallons is unspecified.

- Cost per mile is listed as an output but has no formula and no fuel-price input. A typical formula would be fuel_cost/miles_driven, requiring a currency-denominated fuel price or fill-up cost.

- Trend tracking is claimed but no trend formula, aggregation method, time basis, persistence behavior, or minimum-data requirement is specified.

## Units and conventions

- MPG test values assume miles and US gallons; Imperial MPG would produce a different numeric result.

- L/100km requires liters and kilometers. If distance is entered in miles, convert kilometers = miles×1.609344; if fuel is entered in US gallons, convert liters = gallons×3.785411784.

- Cost per mile requires fuel cost in a defined currency and distance in miles.

- Odometer readings must use the same distance unit for start and end readings; the difference is the driven distance.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "miles_driven": 360,
    "gallons_used": 12,
    "gallon_type": "US"
  },
  "expected_outputs": {
    "MPG": 30
  },
  "working": "1. miles_driven = 360 mi.\n2. gallons_used = 12 US gal.\n3. MPG = miles_driven ÷ gallons_used.\n4. MPG = 360 ÷ 12 = 30 MPG."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

The formulas have no input validation for zero denominators or physically invalid fill-up data. Zero fuel makes MPG undefined (or Infinity in plain JavaScript), and zero distance makes L/100km undefined.

## Other records

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