Source: https://guthlabs.ai/docs/instruments/travel-currency-tip-rounding-helper/implementation/

instrument implementation / implementation-contract

# Travel Currency Tip/Rounding Helper implementation

A source-bound implementation contract for Travel Currency Tip/Rounding Helper; 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**: t7-098

**Effect**: Computation or source lookup only

## Input and validation requirements

The specification provides no concrete country/service lookup data or definitive rounding convention, so results are not uniquely reproducible. Checked arithmetic also fails on sufficiently large bills unless non-finite totals are rejected.

## 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": {
    "bill": 85,
    "currency": "USD",
    "destination_country": "United States",
    "region": "general",
    "service_type": "restaurant",
    "rounding_denomination": 1
  },
  "expected_outputs": {
    "suggested_tip": 17,
    "unrounded_total": 102,
    "rounded_total": 102
  },
  "reference_data": {
    "country": "United States",
    "region": "general",
    "service_type": "restaurant",
    "local_norm_decimal": 0.2,
    "local_norm_percent": "20%",
    "rounding_denomination": 1,
    "rounding_rule": "nearest USD 1.00, half-up",
    "source_convention": "widely tabulated standard value (travel-guide consensus, 2024; culturally variable)"
  },
  "working": "local_norm = 20% = 0.20. tip = 85.00 × 0.20 = 17.00 USD. unrounded_total = 85.00 + 17.00 = 102.00 USD. rounding units = 102.00 ÷ 1.00 = 102 exactly. rounded_total = 102 × 1.00 = 102.00 USD. The 20% norm and the resulting 17.00 USD tip land exactly on the supplied table convention."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/travel-currency-tip-rounding-helper/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/travel-currency-tip-rounding-helper/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/travel-currency-tip-rounding-helper/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-tranche7/tranche7-results.json`