Source: https://guthlabs.ai/docs/instruments/time-zone-converter/implementation/

instrument implementation / implementation-contract

# Time Zone Converter implementation

A source-bound implementation contract for Time Zone Converter; 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**: t7-039

**Effect**: Computation or source lookup only

## Input and validation requirements

- A local source time during a spring-forward gap, such as 2024-03-10 02:30 in America/New_York, does not exist; the instrument must reject it or document a defined adjustment.

- A local source time during a fall-back overlap, such as 2024-11-03 01:30 in America/New_York, occurs twice; the instrument must require a fold/occurrence choice or document its default.

- Missing source date makes DST-aware conversion impossible or ambiguous.

- Named zones, fixed offsets, and abbreviations are not interchangeable; abbreviations such as CST and IST are ambiguous and should not be accepted as zone identifiers without clarification.

- If the native operating-system tz database differs from the documented version, historical and future results may differ; the app should expose or document the data source/version.

- Conversion across date boundaries must preserve the date, not only the clock time.

- Invalid IANA zone identifiers and malformed local date-times require explicit validation and error handling.

## 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": {
    "source_time": "2024-07-01T12:00:00",
    "source_zone": "America/New_York",
    "target_zones": [
      "Europe/London"
    ]
  },
  "expected_outputs": {
    "Europe/London": {
      "local_time": "2024-07-01T17:00:00",
      "utc_offset": "+01:00",
      "abbreviation": "BST"
    }
  },
  "reference_data": {
    "source_zone_row": {
      "zone": "America/New_York",
      "utc_interval": "2024-03-10T07:00:00Z through 2024-11-03T06:00:00Z",
      "utc_offset_seconds": -14400,
      "abbreviation": "EDT",
      "dst": true,
      "source_convention": "IANA tzdata 2024a TZif data"
    },
    "target_zone_row": {
      "zone": "Europe/London",
      "utc_interval": "2024-03-31T01:00:00Z through 2024-10-27T01:00:00Z",
      "utc_offset_seconds": 3600,
      "abbreviation": "BST",
      "dst": true,
      "source_convention": "IANA tzdata 2024a TZif data"
    }
  },
  "working": "New York local time = 12:00. Convert to UTC: 12:00 - (-04:00) = 16:00 UTC. Convert UTC to London: 16:00 + (+01:00) = 17:00. Therefore the result is 2024-07-01 17:00 BST."
}
````

## Other records

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