Magnetic Declination Lookup implementation

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

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