Source: https://guthlabs.ai/docs/instruments/jet-lag-planner/implementation/

instrument implementation / implementation-contract

# Jet Lag Planner implementation

A source-bound implementation contract for Jet Lag Planner; 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**: t4-175

**Effect**: Computation or source lookup only

## Input and validation requirements

The arithmetic itself has no division-by-zero trap, but the specification does not define a precise light-exposure algorithm or an unambiguous sign convention for bedtime shifts. Consequently, concrete light timing and consistently signed schedules cannot be generated without additional conventions.

## 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": {
    "home_zone": "America/New_York",
    "destination_zone": "Asia/Tokyo",
    "travel_date": "2026-04-10",
    "home_utc_offset_hours": -5,
    "destination_utc_offset_hours": 9,
    "direction": "eastward",
    "timezones_crossed": 14
  },
  "expected_outputs": {
    "days_to_adjust": 14,
    "bedtime_shift_hours_per_day": -1,
    "bedtime_shift_direction": "earlier",
    "light_exposure": "undetermined_by_spec"
  },
  "working": "UTC-offset difference = 9 - (-5) = 14 hours. Eastward rate = 1 timezone/day. Days to adjust = 14 / 1 = 14 days. Bedtime shift = 1 hour/day earlier, represented as -1 hour/day."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/jet-lag-planner/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/jet-lag-planner/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/jet-lag-planner/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`