Source: https://guthlabs.ai/docs/instruments/road-trip-cost-splitter/implementation/

instrument implementation / implementation-contract

# Road Trip Cost Splitter implementation

A source-bound implementation contract for Road Trip Cost Splitter; 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**: t4-115

**Effect**: Computation or source lookup only

## Input and validation requirements

The equal-split formula is undefined when num_people is zero. The mileage-weighted formula also requires a nonzero total_miles; zero total mileage would create another undefined division.

## 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": {
    "mode": "equal",
    "total_cost": 120,
    "currency": "USD",
    "num_people": 4
  },
  "expected_outputs": {
    "amount_owed_per_person": [
      30,
      30,
      30,
      30
    ]
  },
  "working": "per_person = total_cost / num_people = 120 / 4 = 30. Each of the 4 passengers owes $30."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/road-trip-cost-splitter/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/road-trip-cost-splitter/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/road-trip-cost-splitter/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`