Source: https://guthlabs.ai/docs/instruments/magnetic-declination-lookup/implementation/

instrument implementation / implementation-contract

# Magnetic Declination Lookup implementation

A source-bound implementation contract for Magnetic Declination Lookup; 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**: t7-026

**Effect**: Computation or source lookup only

## Input and validation requirements

The specification is not numerically executable: it identifies WMM2025 as a required data dependency but supplies neither coefficients nor lookup values. It also does not define pole handling, exact model-validity enforcement, or sign and longitude conventions. A production implementation can therefore return fabricated values, silently extrapolate an expired model, fail at the geographic pole, or report the opposite declination sign.

## 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": {
    "latitude_deg": 0,
    "longitude_deg": 0,
    "altitude_m": 0,
    "date_decimal_year": 2025
  },
  "expected_outputs": {
    "declination_deg": -4.2,
    "annual_change_deg_per_year": 0.06
  },
  "reference_data": {
    "rows": [
      {
        "latitude_deg": 0,
        "longitude_deg": 0,
        "altitude_m": 0,
        "date_decimal_year": 2025,
        "declination_deg": -4.2,
        "annual_change_deg_per_year": 0.06
      }
    ],
    "source_convention": "NOAA/NGA WMM2025-derived tabulation; WMM geodetic coordinates, east-positive declination"
  },
  "working": "Exact table-row lookup. declination = -4.20 degrees. annual change = +0.06 degrees/year. No interpolation is performed."
}
````

## Other records

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