Source: https://guthlabs.ai/docs/instruments/heat-index-apparent-temperature/implementation/

instrument implementation / implementation-contract

# Heat Index (Apparent Temperature) implementation

A source-bound implementation contract for Heat Index (Apparent Temperature); 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**: t4-267

**Effect**: Computation or source lookup only

## Input and validation requirements

An unchecked extreme input causes JavaScript floating-point overflow and a NaN heat index, so the instrument must reject out-of-domain magnitudes before evaluating the polynomial. The unit ambiguity also demonstrates that an omitted temperature unit can materially change the result.

## 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": {
    "air_temperature_F": 90,
    "relative_humidity_percent": 60
  },
  "expected_outputs": {
    "heat_index_F": 99.6778,
    "heat_index_C": 37.5988,
    "risk_category": "Extreme Caution"
  },
  "working": "T=90, R=60, T²=8100, R²=3600, TR=5400, T²R=486000, TR²=324000, T²R²=29160000. HI_F = -42.379 + (2.04901523×90) + (10.14333127×60) - (0.22475541×5400) - (0.00683783×8100) - (0.05481717×3600) + (0.00122874×486000) + (0.00085282×324000) - (0.00000199×29160000) = -42.379 + 184.4113707 + 608.5998762 - 1213.679214 - 55.386423 - 197.341812 + 597.16764 + 276.31368 - 58.0284 = 99.6778179°F. HI_C=(99.6778179-32)×5/9=37.5987877°C. 99.6778°F is in the 90–102°F Extreme Caution band."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/heat-index-apparent-temperature/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/heat-index-apparent-temperature/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/heat-index-apparent-temperature/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`